Retool

Everything can be changed! Done for a variety of reasons, ranging from poor Ratings to someone leaving the show to network fiat, but basically means everything (premise, casting, setting, tone, writing, general emphasis) can be "tweaked" to take the show in a different direction. Not everything changes; some retools are subtle, some not so much. Drastic retooling runs the risk of alienating the current viewership ("change is bad!"), if any.

Many examples of retooling come between when a show's pilot and the episodes made after the series is picked up. Others happen when a show isn't really getting off the ground or is in decline and the creators want to shake things up. When done out of nowhere in the middle of the show, then you've got yourself a Wham! Episode. A retool may also be the result of a Post Script Season; the series ends up going in a strange new direction because all the prior conflicts were already resolved, and new ones need to be invented.

In many cases a retool is needed because as it existed previously, there might have been very little room for characters to grow or that the established rules hindered creative stories. In some cases, when the retool is so drastically different, you are asked to accept what came before in Broad Strokes. Quite frequently, a retool will include one (or more) Tone Shifts.

The most extreme form of retool is the Continuity Reboot.

See also: Retcon, Revision, Rewrite.

Anime and Manga

 * Pokémon began doing this after the Johto saga, when Ash would leave most of the Pokémon he carried with him at Professor Oak's and travel to the new region with just Pikachu. This is meant to create room on his team for Pokémon from the latest generation of games.
 * They did it once more for Best Wishes by having Ash catch more then six Pokémon at a time and putting them into rotation.
 * In addition, they made Team Rocket far more threatening then in previous sagas where they were everyone's Butt Monkeys

Comic Books

 * Marvel Universe heroine Patsy Walker has gone through numerous retools. Started out as an Archie-style teen comedy, moved over into more straight romance, became a superheroine named Hellcat, became Darker and Edgier, and now is... Just weird. And Awesome. Note that all of that stuff is still technically in-continuity.
 * By 1970, X-Men was an unpopular series that was reduced to reprinting old material. 5 years later, after getting a new writer, putting most of the old team on a bus (temporarily) in favor of other characters, and dedicating as much time to Character Development as fights, the series picked up a great many new fans.
 * The Marvel Comics series Thunderbolts has always fundamentally had the same premise (a super hero team (that term used loosely) comprised of villains). However, the exact nature of the team has been changed several times, amazingly with the series lasting over 150+ issues only once being canceled and relaunched once.
 * Originally, Thunderbolts centered around a team of heroes that were actually Baron Zemo's Masters of Evil in disguise working to gain the public's trust so they could easily overtake them.
 * Eventually, the team (those that decided to reform and be actual heroes) came under leadership of Hawkeye up until, a short period where all the previous story lines were abandoned and the book was made into a Super hero fight club. Shortly after that it was cancelled.
 * It was brought back soon after around the time of 'New Avengers' release with a cast featuring some new characters as well as old ones until the Marvel crossover event Civil War.
 * During and after Civil War the team consisted of more popular villains like Green Goblin, Venom, and Bullseye working as "hero hunters" for the pro-registration side to capture anti-registration superheroes.
 * During Dark Reign most of the hero hunter team became the Dark Avengers and the Thunderbolts became Norman Osborn's personal hit squad.
 * Finally, after Dark Reign and at the onset of Marvel's Heroic Age the Thunderbolts are now the super villain prison known as The Raft's rehabilitation program for super criminals (this time including Man-Thing, Juggernaut, and Ghost among others) under the supervision of Luke Cage, Hero for Hire.
 * It has been announced that with issue 175, the book is being renamed to Dark Avengers with characters from the second incarnation of the Dark Avengers joining the cast, still under the leadership of Luke Cage.
 * In the pages of Superman during 1971, an experimental "Kryptonite-Engine" made to provide cheap electrical power malfunctions, causing all the Kryptonite on the planet to become ordinary iron. Meanwhile, Clark Kent became a TV news reporter while an Evil Twin of Superman made of sand drained him of some of his powers. You can read the full saga here. After the entire story is resolved, the series's new direction was quickly lost and more Kryptonite arrives from space, the only holdover from the storyline (until Crisis on Infinite Earths) being that Clark works at a television news station.
 * By 1968, the Metal Men were among the Denser and Wackier of DC Comics' output. That all changed in Metal Men #33, which began a Story Arc where the team could not control their increased powers and find themselves hunted by humans, who turned against them. It came to a head in #37, where the Metal Men were finally apprehended and left for dead in a junkyard. Mister Conan salvaged them and gave them human identities so they could continue to help the world in secret.
 * Recently, in the wake of  the Fantastic Four has undergone a (probably) temporary change with them becoming the Future Foundation. This has involved them donning black and white uniforms, adding Spider-Man to the team , bringing   along for the ride and becoming a sort of superhero think tank. Thus far the new series has been well received.
 * In the late-1980s, Steve Engelhart tried to spruce things up with the 'NEW' Fantastic Four, with Reed and Sue Put on a Bus and replaced with Crystal and the second Ms. Marvel.
 * DC's September 2011 relaunch currently stands with one foot in the Continuity Reboot camp and another in the retool camp. Some characters are getting retold origins and backstories (Superman is getting his early days retold, with him now being the first superhero in the DCU) while others are simply getting a change to the status quo (Bruce Wayne is now the only Batman, with Dick Grayson going back to Nightwing and Damian remaining as Robin).
 * Katy Keene had two revivals, each retooling the story their own ways.

Film

 * The Star Trek franchise features several notable film examples:
 * Star Trek II: The Wrath of Khan retooled the franchise after the mediocre results of the first movie, by bringing back a classic villain and retooling Starfleet as more naval-oriented than it was portrayed in the original series.
 * The 2009 Star Trek retooled the entire franchise after the dismal box office results of Star Trek: Nemesis. The focus was changed to a different timeline following the (now changed because of ) adventures of the crew from the original series.
 * Star Trek: First Contact radically redesigned the Borg in many ways. The most obvious one is cosmetic, they looked like they were being rotted out from the inside whereas their prior makeup was pale guys in armored suits. They then established the idea of the Borg Queen because without a leader they are really just slightly more difficult zombies. Then it showed that they assimilate people en mass as well as technology, whereas in the TNG "Best Of Both Worlds" it was suggested that Picard was a one time deal. And lastly, partially because of the existence of the Queen, they are shown to have a much greater sense of tactics and strategy to even attempt the Time Travel plot, before they were just overconfident in their malevolence. But there is a reason First Contact is considered the best TNG movie.
 * The Rocky series was retooled in the third movie to be more action-oriented and contain less drama. The fifth Rocky film went back to its roots. The sixth film made over a decade later went for drama with a more realistic push.
 * After Batman Returns came under fire from parents, watchdog groups, and merchandise-tie-in companies such as McDonald's for being considerably darker, more violent, sexual and disturbing than its 1989 predecessor (as well as not even getting remotely close to equaling its box office intake), director Tim Burton as well as star Michael Keaton and composer Danny Elfman left the series. In their place for the Lighter and Softer (as well as brighter) third movie, Batman Forever came Joel Schumacher, Val Kilmer and Elliot Goldenthal respectively.

Live Action TV

 * This has been done several times in Alias. In one episode during a later season, an overarching storyline is resolved, Sydney finally admits her love for Vaughn, and the show's premise fundamentally changes as a result.
 * After its cancellation and renewal, Battlestar Galactica was retooled into Galactica 1980, which proved so unpopular that many fans of the original show refuse to acknowledge its existence.
 * And it was rebooted completely with the reimagining of the series which turned away from the Narm Charm of the original for a dark and twisted storyline with heavy philosophical themes and social-political commentary.
 * Ironically, at the same time Galactica was being cancelled, Buck Rogers in the 25th Century, which aired opposite it, was retooled to make it more like Galactica. The second season of Buck Rogers was a departure from Buck and Wilma protecting Earth from evil. In the second season, Buck, Wilma, and Twiki were stationed aboard a research vessel, but their adventures were somewhat similar to the first season, though some of the main characters were replaced by others, like Buck's new sidekick, Hawk.
 * The Bill has undergone several in its 26+ year lifespan. The most dramatic were in 2002 (when 7 of the regular long standing cast members were killed off in a single episode), and 2009 (when the series moved to HD, started being broadcast after Watershed, and completely replaced its theme music with a different tune for the first time ever).
 * The first season of Blackadder had Blackadder as a simpering coward and borderline Butt Monkey, and Baldrick as Hypercompetent Sidekick - his "cunning plans" actually tended to be cunning. From the second season onward, Blackadder became the Deadpan Snarker that the show is best known for; and Baldrick became a classic Bumbling Sidekick. The result was a much funnier show.
 * This was actually a retool of a retool. The original pilot for Blackadder featured the characters being much closer to those in the second series. It was only after the objections of Rowan Atkinson (who felt they hadn't provided him with an actual character) that the characters were changed around.
 * CBS' primetime drama Central Park West suffered this. The show was originally about a pair of siblings who immersed themselves in the world of high-class socialites, and got caught up in all the backroom deals and intrigue that followed. In the second season, the theme song was changed (from a sultry and mysterious jazzy song to the type of theme you'd hear on a cheesy soap opera), the show was marketed as "CPW", half the cast was jettisoned (including one of the two siblings), Raquel Welch was cast as an Alexis Carrington-esque business owner, and many story arcs were dropped. However, it could be said that the show immediately improved as a result of this retool (especially since the writers dropped the pretenses and started having fun with the material). Then, it was cancelled shortly thereafter.
 * Charles in Charge was retooled when it moved from network TV to syndication, discarding Charles' original employers and girlfriend and replacing them without changing the house where he worked -- and managing to maintain a single continuity through the process.
 * Throughout the three series of Chef!, only three actors remained constant, although this was explained in the first episode (Le Chateau Anglais had a high turnover rate), but the third season seemed a real departure from the previous tone, as Gareth's wife left him, a man from Oop North bought the restaurant off of him, an American was added to the primary cast (although one had previously appeared in the first season), the soundtrack got a bit worse, and the entire kitchen staff started to develop personalities. Nevertheless, managed to be an example of a successful retool.
 * Coach had Hayden Fox leave Minnesota State University to coach a pro team in Orlando in Season 8.
 * Buffy the Vampire Slayer introduced several new characters and a college setting, leaving most of the background characters from high school behind, after Angel, Cordelia, and Wesley left Sunnydale in the third season finale to create a Spin-Off. It was retooled again in the sixth season, emphasizing that Buffy had to take on the role of an adult now and there was no school at all.
 * Angel was retooled after the first season, which was heavily Film Noir supernatural detective style and became much more modern fantasy oriented. The fifth season showed a dramatic change with the main characters becoming the operators of their enemies' law firm at Wolfram and Hart, including near limitless resources.
 * The original series of Doctor Who thrived on this. The most comprehensive and obvious retool was between the 6th and 7th seasons when all three regulars decided to leave at the same time, the show changed to colour from black and white, and the Doctor was given a whole new backstory and exiled to Earth. The wiping-out-from-all-of-existence of the Time Lords between the show's 1989 cancellation and its 2005 resurrection might also be considered a retool. (Actually, the introduction of the Time Lords counts as a bit of re-tool in itself. Originally the Doctor simply came from a mysterious alien civilization, with no more details offered.)
 * Even earlier then that, the show was retooled from an educational show to the scifi story it is today. Originally it was supposed to alternate between historical stories set in the past, and scientific ones set in space (which is why the first two companions were a history teacher and a science teacher). The beginnings of the shift appear as early as the second serial, and it was the popularity of the Daleks that led to the educational format (and most of the historical aspects) being abandoned in favor of pure Scifi.
 * Not to mention regenerating the main character at irregular intervals, with attendant changes of appearance and personality.
 * Earth: Final Conflict did more or less the same thing. Twice, at least -- more (at least once an episode in the second season), if you consider violent changes in tone to be tantamount. The biggest change was killing off the lead character to make way for a new hero.
 * The Electric Company is back and updated for the late 00s -- filled with rapping kids with superpowers fighting bad guys, Mind Control plots, and other elements that reek of Executive Meddling. Even Joan Ganz Cooney, the creator of Sesame Street, doesn't think it's all that good.
 * The Channel Five soap Family Affairs had several retools. The first one got rid of the eponymous family entirely, and later ones were even more drastic. None of them seemed to help the ratings, though.
 * The 2007 Flash Gordon series was retooled during a mid-season hiatus to combat highly negative fan reactions; the Monster of the Week format was abandoned in favor of an arc-based storyline, Flash's Black Best Friend was dropped from the cast, and much more screen time was spent on Mongo in general. Arguably, the show got better as a result.
 * After the death of Dolph Sweet, Gimme A Break was given a massive overhaul. The two older daughters were dropped, the rest of the cast moved from the California suburbs to New York City, and Joey was given a younger brother (played Joey Lawrence's younger brother, Matthew). And even that was tweaked in the final season, with Samantha, Grandpa Kiniski and the new NYC neighbors leaving, and Nell's mother, Addele, moving in.
 * Hearts Afire changed its setting and most of its supporting cast for its second season.
 * The Jeff Foxworthy Show explored this in a series of commercials between seasons. Jeff and his TV son are discussing where they have been recently and why everything is so strange. Jeff calmly explains that the network is retooling their show so it will be even better and his son shouldn't worry. When the boy asks where his Mom is, Jeff tells him that she is being recast.
 * Kamen Rider Hibiki experienced a massive retool about 30 episodes into the 48 episode series. The show, never intended to be a Kamen Rider season to begin with, was very different in terms of what it was doing, and took a while to grow on people, so the retool was an attempt by executives to bring the show more in line with what a "normal" Toku show was supposed to be. However, when the retool hit, people began to realize how much they loved the original version. Fans, critics, and even the cast itself pretty much hated the changes, and the executives that had ordered it all got lambasted for their gross mishandling of one of Toei's premier franchises.
 * Knight Rider (2008) received a massive retool, dropping the government organization aspect and losing 3 cast members (in the space of two episodes) in a horribly anti-climactic KARR plot 12 episodes into the first season. This arguably improved the show quite a bit and focused on more personal stories, more closely resembling the original show in structure. Then it wasn't renewed.
 * When Laverne and Shirley moved from Milwaukee to Los Angeles. They took their dad, Lenny, Squiggy, and Carmine with them.
 * Struggling soap Loving moved from its suburban setting to New York City and became The City. The retooled version wasn't any more successful than the original, and the show was soon cancelled.
 * After the first season of Major Dad, the setting was moved to a different military base, with some changes in the cast.
 * Millennium was retooled twice, with the result that the eponymous Millennium Group is completely different in each of the three seasons; an unassuming law enforcement consultant group in the first season, an enigmatic but good-intentioned Ancient Conspiracy in the second season, and an unambiguously evil Ancient Conspiracy in the third.
 * After Mystery Science Theater 3000 moved to the Syfy with their eighth season, they got new villains, a new setting, and (due to Executive Meddling) an actual ongoing plot. At the end of the season, some of these changes were backed off on, with a move to a setting similar to the first seven seasons and a lack of stories that carried on between episodes (though the 10th season had a subplot that was dropped halfway through).
 * Red Dwarf has arguably done this four times in eight seasons: the addition of Kryten and the female Holly in season 3, as well as changes in production staff who made the budget stretch much further; the loss of the eponymous spaceship in season 6, leading to much of the action taking place in a single cockpit; the switch to film-like visuals and a more comedy-drama feel in season 7, plus the departure of co-writer Rob Grant; and the almost complete reboot in season 8, when the whole spaceship and crew were recreated as they had been 3 million years previously.
 * The 5th season of Sabrina the Teenage Witch moved Sabrina to college, introduced several new characters and dropped others. The 7th season dropped the college setting and again dropped and added significant characters.
 * Saved by the Bell was retooled after a brief cancellation. The school moved from Indiana to California, and the show even had a name change (it was originally known as Good Morning, Miss Bliss) as well as a few different cast members and a new focus on the students exclusively.
 * It was retooled again after the gang graduated and moved on to California University. In addition to the new setting and a few new characters, the stories became somewhat more "grown-up." The new show didn't make it to a second season.
 * In the 9th season of Scrubs, The series moves from Sacred Heart Hospital to a medical school and the focus characters become the new students.
 * Second Chance, an early Fox network offering, was about a man stuck between Heaven and Hell, who got the chance to visit his younger self (played by a pre-Friends Matthew Perry) to alter the course of his life. The series failed miserably, but the network attempted to build on Perry's charm by retooling the series as Boys Will Be Boys, dropping the afterlife angle and instead focusing on Perry's character and his best friend. The retooled version didn't fare much better.
 * The computer tech show The Screen Savers that ran on Tech TV then G4 after the merger was retooled as Attack of the Show; a more geek and nerd entertainment focused show keeping the same hosts -- at the time, Sarah Lane Kevin Rose and Kevin Pereira as well as Brendan Moran. The user created challenge from the last The Screen Savers episode was carried over to the first Attack of the Show where the winners were revealed.
 * For its ninth season, Stargate SG-1 received new characters, arcs, and villains, generally refreshing and refocusing the show.
 * The Star Trek television franchise has done this on several occasions:
 * Star Trek: The Original Series was retooled to be more action-adventure-oriented after the original pilot, "The Cage", was thought too cerebral by network executives. Most of the crew was recast as well, with Leonard Nimoy and Majel Barrett being the only actors from "The Cage" to make it on to the actual show. And that's with Barrett playing a different character on the show than in "The Cage".
 * Star Trek: The Next Generation did this in the transition between its first and second season (see Growing the Beard). The supporting characters started to find their niches, the bridge set was slightly redesigned, characters including Worf and Laforge were promoted, and Diana Muldaur came on as the new doctor, Pulaski.
 * The third season dropped Pulaski and brought back Dr. Crusher, but it was also defined by the new uniforms that were more comfortable for the actors (being two pieces instead of jump suits) and had a more professional look to them having high collars.
 * The season three finale/season four opener could also count with the introduction of the Borg as a major threat. The series gets just a hair Darker and Edgier and lets Picard have a delayed and well deserved Heroic BSOD about being assimilated.
 * Star Trek: Deep Space Nine brought in Worf in the fourth season and redirected the story towards a new Klingon conflict. While it was due to Executive Meddling, it was considered a successful integration and helped further their Dominion Story Arc by revealing the Klingons were being manipulated by them.
 * Star Trek: Voyager underwent a retool in its third season because of the long-running Kazon plotline. The Season 3 premiere, "Basics Part II" effectively ended their storyline because Paramount executives complained that it wasn't exciting enough. In Season 4, the show was retooled again by swapping out Jennifer Lien for Jeri Ryan, and introducing Species 8472 and the Hirogen as new threats.
 * Star Trek: Enterprise was retooled twice in response to bottomed-out ratings, and consecutively no less. The first retool occurred in Season 3 and abandoned the Plot of the Week for a season-long "epic" story arc. When that failed, the show was retooled for Season 4 by bringing in new creative staff and focusing the season on two or three-episode long mini-arcs. Although the quality of the show improved significantly (Season 4 is usually considered the best of the show), it was too little too late and said season proved to be its last.
 * Thomas the Tank Engine had a minor retool in Series 5 when it stopped adapting the Railway Series stories it had previously been based on. A further retool was in Series 8 when a new theme song and story format was bought in, and many characters such as Duck were dropped with no explanation.
 * In 2009, the series dropped models and created new episodes exclusively in CGI.
 * The third series of Torchwood took a sudden turn into bleakness, and became a politically charged miniseries as opposed to the episodic structure.
 * And the fourth series moves the primary setting to America, and turns Torchwood into more of a resistance movement as opposed to a short-staffed special ops.
 * The title character of Valerie was killed off, and her place filled by Sandy Duncan, with the name of the series changed to The Hogan Family. A rare case of a Retool centered around a Suspiciously Similar Substitute.
 * To say that the second season of the 1980's War of the Worlds TV series used some "creative liberties" during its second season would be stating it lightly. Half the cast either disappeared (General Wilson) or were killed off (Colonel Ironhorse, Norton Drake), the main antagonists of the first season were unceremoniously executed, a new group of aliens took their place as the villains, the setting changed from a mansion to a sewer base and the entire style of the show changed from a somewhat lighthearted, highly cerebral communism metaphor into a dystopian near-future proto-cyberpunk survivalist fantasy. The fans were not pleased.
 * Newhart underwent a major change when Kirk and Leslie were written out and Michael and Stephanie were written in. This corresponded with the show becoming more surreal.
 * After its first season, The Odd Couple switched to a three-camera format, with a new set and a live audience. Most characters left over from the movies (the Pigeon sisters, Oscar's poker buddies) were jettisoned, with the exception of Murray.
 * Here's an example that set a record: the premiere of the Game Show You're in the Picture proved that the game was too awkward to be enjoyable. The second episode was completely different: it consists of the show's host, Jackie Gleason, sitting in a bare set and making a drawn out apology for the failed gameshow. This received much better reviews, so the show was turned into a talk show and renamed The Jackie Gleason Show.
 * Each season, Prison Break went through went through a dramatic change in tone and style, though the main cast and the overarching story continued throughout the series. Season 1 is comparable to Escape from Alcatraz, season 2 is The Fugitive, season 3 is Midnight Express (or at least, that's what the writers were shooting for) and season 4 is Mission Impossible.
 * Naturally, Sadie was re tooled after the first season with changes including Arden replacing Chelsea as the Alpha Bitch, bringing in a new romantic interest for Sadie, and even changing Sadie's character.
 * Bob Newhart's third series Bob! was the story of Bob McKay, a greeting card artist who had a few decades earlier created a semi-successful comic book character called "Mad Dog". When Ace Comics offers him a chance to revive the book he quits the greeting card company and deals with the wacky people who work for the comic book company. After the first season the series was renewed, but in the first episode of the second season it is explained that Ace Comics went out of business and Bob crawled back to the greeting card company to get his job back there (and deal with the wacky people there). This version only lasted a few episodes before it was canceled.
 * It's About Time was a series created by the creator of the then current Gilligan's Island, and featured that show's slapstick approach. The storyline concerned two Astronauts whose space capsule goes backwards in time and lands in a time of cavemen. Storylines dealt with the astronauts bringing civilization to the local cavepeople, while at the same time trying to fix their spaceship. At the midpoint of the show's first (and only) season the astronauts manage to fix their ship and leave the stone age, only to find that two of the cave people who helped them stowed away on the ship, flipping the storylines to episodes involving the astronauts hiding the cave people from the government while helping them adapt to 20th Century life. The catchy series theme which explained the premise was cleverly flipped and adapted to this for the second half of the season.
 * Robin Hood was retooled after the Wham! Episode at the end of Season Two in which Marian and Will Scarlett and Djaq (the Saracen) are written out of the show. Along with a new writing team and new costumes for the cast, five new characters were introduced to the show (three of whom were not even part of the Robin Hood legend) and the premise goes from robbing the rich/feeding the poor to a fight for power over the position of Sheriff as well as Robin's tangled love-life with two new love interests. The three original remaining outlaws become bit-parts, and all of the storylines of the past two seasons become Aborted Arcs. In fact, one could go so far to say that if it were not for the character names and the locations, there is little in Season Three that connects it to the legend of Robin Hood at all.
 * Suddenly Susan was a comedy about a career-minded woman who works as a writer with a local newspaper. During the jump from the third to fourth seasons, several characters disappeared (including Susan's boss, who she had previously admitted being in love with and a newspaper employee [which was caused by the actor who played him killing himself]), the introduction of a new boss and an overhauled office setting. This retool wasn't really motivated by ratings either, as they had stayed relatively consistent. However, the show was cancelled soon afterwards.
 * McHales Navy moved to the Italian theater of WW 2 in its final season.
 * When the spy craze overtook TV in 1965, the detective series Burkes Law was turned into Amos Burke, Secret Agent.
 * The Facts of Life dropped half the cast after the first season (although some of the girls popped up on occasion during the 1980-1981 season), added Jo to contrast with Blair, and most importantly got better writers. (Even the theme song improved!)
 * In addition, there were three major settings throughout the run. At its heart, the main setting always remained at (or near) the campus of Eastland School, but starting in 1983, much of the action shifted to a gourmet bakery called Edna's Edibles. By 1985, with the core group of girls (Blair, Jo, Natalie and Tootie) in their late teens or early 20s, the girls now began managing a novelty store called Over Our Heads; the explanation for that shift was that a kitchen fire (Off Screen) destroyed Edna's Edibles.
 * Another re-tool was planned for the 1988-1989 season, with series star Lisa Welchel being one of the few cast members opting to stay for the to-be-retitled series. The action was to shift back to Eastland, now a co-educational school (done so on Blair's action to save the financially starved school from closing; as she was extremely wealthy, only she had the financial resources to pull off such a move). The set-up was aired in a two-part Facts episode, "The Beginning of the End/Beginning of the Beginning" (highly reminiscent of the original Facts pilot, "The Girls School," which aired as a Diff'rent Strokes episode back in 1979), but the series never made it to air. Had the series been green-lighted, Facts (and its new name) would easily have been NBC's longest-running sitcom at that time.
 * Charmed had a change after the third season due to Shannen Doherty's departure from the show and Rose McGowan was added to the cast as fourth sister Paige, and the dynamic changed with Piper now being the eldest, Phoebe being the middle child, and Paige acting as the youngest. The opening credits were also changed with Alyssa Milano receiving first billing and Holly Marie Combs getting the "and [insert name] as [character]". There was another retool for the final season which had the character of Darryl written out; new characters Billie, Christy, Coop, Dex, and Henry introduced; and the temporary departure of Leo mid season until the finale. Also Phoebe started wearing actual clothes.
 * ABC's Too Close for Comfort starred Ted Knight as a newspaper cartoonist who lived and worked in San Francisco with his wife and two grown daughters. When the show moved to first-run syndication in its final season, it was retitled The Ted Knight Show, Knight's character moved to suburban Marin County and changed his job to co-owner and editor of a newspaper, and his daughters vanished without a trace...although Jim J. Bullock's Breakout Character Monroe, originally the boyfriend of one of the daughters, was retained after the retool.
 * I Love Lucy had a temporary retool in the fourth season when Ricky gets a starring role in a movie and he and Lucy and the Mertzes go to Hollywood and stay at a hotel. They move back to New York City early the next season. In the sixth season the Ricardos move to Connecticut and are followed by the Mertzes. In the seventh season the show becomes the The Lucy-Desi Comedy Hour becoming an hour long show with a special guest star each week.
 * In the first season (1967-68) of Mannix the title character worked for a detective agency called INTERTECT that utilized state-of-the-art (for it's time) computer equipment to solve crimes. However, Mannix generally disregarded the computers and the agency's rules to solve crimes his own way. Lucille Ball (Mannix was the last show produced by Desilu) decided that the computers were over most viewers' heads and asked to have them worked out of the show. This turned Mannix into a more conventional detective series. The font used in the credits were based on IBM's corporate font of the time. That font and the theme music were about the only things that transitioned over into the new version of the series.
 * In season one, the Mannix title card is literally a computer card.
 * Season two and beyond (1968-75), with the better known title card with the shifting letters.
 * The Avengers was originally about a doctor teaming with a mysterious secret agent named John Steed and their investigation into crimes. In the second season the actor playing the doctor left and Steed became the lead. Steed then gained a new partner, the leather-clad, judo-knowing Cathy Gale, the first Action Girl of many that Steed would be partnered with through the decade. After her would be the most famous to American audiences, Emma Peel and finally Tara King.
 * The first season of Wonder Woman, was set during World War II with Wonder Woman battling mostly Nazi or Axis foes and her secret identity was WAVES petty officer Diana Prince. The tone was also a little comedic. When the show moved from ABC to CBS, the show became less humor-oriented, the timeframe moved up to the modern era (the late Seventies), and Wonder Woman's secret identity became an agent of a US intelligence organization called the IADC.
 * Martial Law had a rather bizarre case of this: The end of season 1 saw Sammo and Big Bad Lee Hei falling out of a helicopter over the ocean. Sometime during the summer, though, it was decided to retool the show, and instead of season 2 picking up off where the first had ended, it opened with a regular episode, with only scant references to the previous cliffhanger. Fans were not pleased.
 * After two seasons, the live-action Superboy series changed its title to The Adventures of Superboy, and moved the two central characters, Clark Kent/Superboy and Lana Lang, away from college to an internship at The Bureau for Extra-Normal Matters, an X-Files like agency that investigates paranormal phenomena. Along with the title and setting change, the show's stories became darker in tone, and the look of the show became darker as well. Many stories took place at night after the change, and the lighting for the final two seasons was done in a film noir style.
 * Although Power Rangers gets a retool every year with new costumes and mecha (and as of the seventh season onward a new cast) a notable retool took place midway in Power Rangers Turbo when 4/5 of the main cast was changed over for a new cast. This was done to save Power Rangers from failing ratings. It took something more to accomplish that, though. Though the Retool was enough of a ratings boost to warrant another season.
 * Speaking of Space, there was a retool. We leave "kids in high school battle the Monster of the Week and go home" behind and have more arc-based series with the Rangers, well, IN SPACE! and the villains of all past series having formed a Legion of Doom. Part of why it was so epic is that they wanted the franchise to go out with a bang, but by the time it was over, fans underwhelmed by Turbo and then hit with the loss of their favorite characters had forgiven the Seasonal Rot and wanted more. They're still getting it as of 2012.
 * It seems you get the best series when The Powers That Be think it's ending. Power Rangers RPM was also supposed to be the last season.
 * The Naked Truth, a 90's sitcom starring Tea Leoni as a newspaper photographer, was drastically retooled and almost entirely recast each season. In season 1 Nora (Leoni) works at a sleazy celebrity tabloid and had Tim Curry and Amy Ryan for co-stars. Season 2 de-tabloided the paper she worked for and de-zanified the format; only Nora and Camilla (Holland Taylor) remained of the original cast. Mary Tyler Moore and George Segal were added as Leoni's parents. Season 3 saw Nora and Camilla jump ship to another paper with a staff that included Chris Elliot.
 * Who Wants to Be a Millionaire? has gone through countless retools over time on the American version. This includes changing the host from Regis Philbin to Meredith Vieira, adding a clock, changing several of the Lifelines, omitting the "Fastest Finger" round, etc. The 2010-11 season completely overhauled the game even further, adding a new payout structure and randomizing both the question difficulty and payouts.
 * For its fourth and final season Hannah Montana removed Mitchell Musso from the main cast, moved the Stewart family into a bigger house, had Lilly come to live with them, and replaced the series' most-used outdoor set (a generic beach) with a mock-up of Santa Monica Pier. Along with these sweeping changes, the show was renamed Hannah Montana Forever.
 * In a very strange example, Goodson-Todman's 1967-69 Game Show Snap Judgment was changed for its last three months from a contrived word-association game to a direct clone of Password.
 * The first season of 3-2-1 Contact involved a team of college students in a room known as the "workshop". In seasons 2-4, it was changed to a cast of middle school-aged kids in a basement. The last three seasons switched to a location-themed format, focusing more on individual hosts (mainly David Quinn) rather than a team. The theme song was also remixed in the second and sixth seasons.
 * Bergerac, the British cop show, had a bizarre final series in which the lead character relocated to France and became a private eye, to little consequence.
 * Gritty police drama Between the Lines ended series 2 with a very over-the-top Cliff Hanger, so much so that when it returned for series 3, the only way out was to reshape the show with the lead characters.
 * Single-season sitcom Flying Blind went through a major rework halfway through the first and only series, with the male lead leaving his job as an office drone and becoming a Troma-esque underground filmmaker instead.
 * The Event was put on a hiatus in the middle of its first season and retooled due to low ratings. The show stopped using flashbacks to tell the story in an anachronistic style, the villains' motivations were streamlined, and the heroes made more forceful and less indecisive. This turned the show more into a 24 rather than a Lost. The show improved in ratings but was not renewed for a third season.
 * It was justified in-story by the aliens finding out that they were wrong about how much time they had and instead of having decades to work behind the scenes they had mere months to enact their plan and save their race by any means necessary. Their actions became more desperate and destructive, and the more ambiguous characters had to choose where their loyalties really lay. One of the major conspiracy plots is short circuited when the Big Bad
 * Sonny With a Chance is about small town girl Sonny who joins the cast of her favorite sketch comedy show So Random!. Demi Lovato (who played the titular character) ended up quitting the show and taking a temporary break from acting after season two, to deal with some personal problems and also focus on her music career. Disney retooled it by defictionalizing So Random. Yep, the show within the show became the actual show!
 * Shining Time Station was retooled twice at the end of its life. First, while keeping its title, the show became a prime time series that aired in spurts as a series of specials. Unlike the child-pleasing daytime series, this version added elements of teen drama (such as the addition of a juvenile delinquent from an abusive household), and featured extensive location shooting, breaking free of the prior version's omnipresent train station interior. (The new-found sense of maturity was actually referenced on the show, as Mr. Conductor appeared as usual to relate an Island of Sodor story to the kids, only to be told that they had outgrown Thomas stories). After a handful of these episodes, the show returned to daytime under the new title of Mr. Conductor's Thomas Tales, which scrapped the entire cast except for George Carlin as Mr. Conductor, and focused almost entirely on Sodor segments.
 * Human Target got retooled for its second season, with several changes: the cliffhanger of the first season was resolved immediately and then forgotten, the sets got a new, shinier look, and two new female characters were introduced, one of whom was Ms. Fanservice who contributed little, and the other did nothing but question Chance's methods but grudgingly admit they worked every single episode and provide a forced romance. Also, the music went from Bear McCreary sweeping orchestral to generic action music.
 * Boy Meets World got retooled several times of the course of its run:
 * Season 2: Cory, Topanga, and Shawn start going to John Adams High. Mr. Feeny follows them. Eric has a much larger role, and begins to take on traits of his "modern" persona. Topanga abandons her Granola Girl roots and becomes a Hollywood Nerd. Mr. Turner, "the bullies," and Chubbie's are introduced. Also, the show loses Minkus, and abandons the old theme song and credits sequence.
 * Season 5: At the start of their senior year, Shawn reunites with his Long Lost Sibling Jack, who joins the main cast. Shawn, Jack and Eric (now attending college) move in together in an apartment, and Jack becomes Eric's best friend and comedy sidekick. Heretofore Kidanova Shawn gets a steady girlfriend Angela, who becomes a recurring character. Mr. Turner falls victim to Chuck Cunningham Syndrome and main high school set is changed to the senior hallway. The show gains an increased focus on running storylines, something it had already been experimenting with. Finally, the classic Theme Tune (with lyrics!) is introduced.
 * Season 6: Cory, Shawn, Topanga, and Angela graduate and go to Pennbrook University. Mr. Feeny follows them. Angela becomes a member of the main cast. Cory and Topanga get engaged, but don't exactly make a mad dash for the altar. Rachel joins the cast and moves in with Eric (now a full-on Cloudcuckoolander) and Jack, setting up a Love Triangle. Alan, Amy, and Morgan are reduced to Commuting on a Bus.
 * Space: 1999 : Season 1 was rather thoughtful and existential with an atmosphere of both genuine danger and epic grandeur and could almost have been shot in black and white. It featured a huge, multi-level main set, awesome space battles, and a sweeping orchestral score. Season 2 was far more simplistic, fast-moving and colourful, with loads more monsters, comedy robots and running around. Several main characters were ditched without explanation, a shape-shifting alien hottie was introduced, there was more focus on the characters personal relationships, the sets were smaller and more intimate and the score was largely replaced by funky guitar. Even the heroes uniforms were changed, with jackets, mission patches and ID badges added for extra colour and interest.
 * 90s NBC sitcom Jesse (starring Christina Applegate) was, quite typical for its era, about a single woman in her twenties with a major Will They or Won't They? plot, but distinguished itself somewhat by originally featuring the main character's family (wacky brothers and gruff father) in major roles, as all of them worked at the dad's bar together. However, that family vanished in the second season as Jesse got a new job at a hospital with young and attractive colleagues, while her girlfriends got more screentime than in the first season. The producers were obviously trying to make the show more similar to a certain other show of theirs.
 * 24 did a soft Retool in season 4, putting Jack Bauer in a new job (albeit one that still gets him involved in the main action) and ditching most of the main characters from previous seasons in favour of a new Big Good, Voice with an Internet Connection, etc. Unfortunately the writers lost their nerve: by about halfway through the season, Jack was working for CTU again and most of the old cast had returned anyway.
 * Season 7 is where they did the Retool right. The action is moved to the opposite side of the country, Jack is neither a federal agent or a federal fugitive, he's teamed up with a Distaff Counterpart, CTU has been disbanded (its role is mostly filled by the FBI), and the few returning characters either having gone underground or.
 * Eerie Indiana only had one season, but got a retool two-thirds of the way into it that included the addition of John Astin and Jason Marsden.

Magazines

 * After nearly four decades as a knockoff of Mad, Cracked morphed into a "lad mag" akin to FHM or Maxim. This retool was short-lived and the magazine died soon afterward, only to be revived online as the list-heavy humor site it is now.

Newspaper Comics

 * Blondie was originally about a flapper and her rich boyfriends. When she married one of them, Dagwood Bumstead, he was disinherited, had to get a job, and lived a life more of the audience could identify with. On top of that, said husband essentially became the main character.
 * Barney Google moved to a place full of hillbillies, then was written out in favor of Breakout Character Snuffy Smith.
 * Beetle Bailey moved from college to the army very early in the series' run.
 * When Garry Trudeau returned from his 18-month sabbatical, the main characters of Doonesbury left college (and the town the college was in) behind, got careers & families, and started aging in real-time. This caused a noticeable shift in the perspective of the strip (although its political nature never changed).
 * Although at the very beginning, the cartoon wasn't really oriented towards covering politics at all, being about the college life of its main cast and making this a double example.

Western Animation
"Homer: Uh ... so, I just wanna know how come you made your Homer Simpson character so ... Producer: Stupid? [laughs] Well, I can assure you, it happened organically. Homer: It better have!"
 * When Doug moved from Nickelodeon to ABC, many characters and locations were redesigned, and the show was renamed Disney's Brand Spanking New Doug. There were in-show reasons given for most of the changes.
 * This was also played with in-show, with the James Bond Ersatz "Smash Adams", who was retooled into a fat and bumbling secret agent.
 * Spoofed by an ad campaign which aired between seasons of King of the Hill. The second season ended on a cliffhanger with the local Mega-lo Mart (a Wal-Mart Expy) being destroyed by a propane explosion. Four characters, including protagonist Hank, were inside at the time, and FOX told viewers that one of them would die. Ads that aired throughout the summer showed viewers a "behind the scenes" disagreement between Hank and FOX, which threatened to kill him off unless he agreed to allow the show to be re-tooled by moving it to Los Angeles and retitling it "King of the Hollywood Hills." Hank refused, and eventually got his way thanks to Bobby accidentally getting a hold of some compromising photos of a FOX executive. Of course, in reality, there was no such dispute and the writers had always known from the start who they were going to kill off.
 * Spoofed on The Simpsons episode "Homer to the Max" (1999). Watching the first episode of Police Cops, Homer is thrilled to discover he shares his name with its Don Johnson-like lead character (catchphrase: "And that's the end of that chapter!"); the next week Homer is horrified to see his character retooled as a blundering doofus (catchphrase: "Uh-oh, Spaghetti-Os!"). He seeks out the show's producers and writers.


 * Another episode featured a RoboCop Expy. Homer wanted to watch it before it got retooled. A couple of seconds later the robot (who is also a Father) quit the force and got a job at a fashion agency.
 * The '80s-'90s cartoon version of Teenage Mutant Ninja Turtles 1987 was retooled for its eighth season, going through significant changes in audiovisual style and tone. The episodes after the retool are commonly known in the fandom as the "Red Sky Episodes", since this was the hue the backgrounds almost invariably took. The story itself became darker, with the Shredder going from Affably Evil to total Big Bad and more threatening than ever, and the Turtles becoming wanted by the NYPD for.
 * In the ninth season, the series received more changes. Shredder and Krang were Put on a Bus and replaced by Lord Dregg, who would became the main villain for the rest of the series. The Turtles also got a new sidekick named Carter, and there was also a new subplot involving the mutagen, that turned them the way they are at the very beginning, going wrong, turning them into large mutant monsters.
 * Like its predecessor, the second Teenage Mutant Ninja Turtles 2003 animated series was eventually retooled. During its sixth season, its setting was changed from the present day to the year 2105 via accidental time travel. "Fast Forward", as the season was subtitled, featured a shift in art style (simpler) and in tone (lighter), the abandoning of most of the show's supporting cast in favor of completely new ones. A second, milder retool occurred with the seventh season, which featured the turtles' return to present day, yet another Art Shift, and a new subtitle--"Back to the Sewer".
 * Cartoon Network's acclaimed Toonami block received this in 1999, arguably for the better.
 * And then came CNReal. It wasn't successful, though.
 * An In-Universe example in South Park episode "Whale Whores". When Stan Marsh overtakes Whale Wars reality show, he begins some radical actions to save whales and dolphins, but everybody sees it just a retool of the show.
 * Pinky and The Brain was retooled into Pinky Elmyra and The Brain after Executive Meddling forced the annoying Elmyra into the main cast.
 * Ka Blam! got slightly re-tooled in it's second season, giving new personalities to Henry and June, changing the overall look of the characters, and Art Evolution and new theme tunes for some of the shorts. Also, the jokes were less "random" than the first season.
 * The show was also briefly retooled in the fourth season. The comic book-setting was pretty much abandoned (with the exception of "turning the page", though they really couldn't get rid of that, as well as the opening and ending themes), the show's TV studio setting was more apparent, the jokes in the Henry and June segments became less random and more "mature", and most of the "classic" shorts skipped a few episodes.