Instant Plastic Surgery

In the real world, plastic surgery is a long and painful process, with clearly-defined limits on what can be accomplished. Thankfully, in a magical, or sufficiently futuristic setting, things are a lot more simplified; all you need is the right spell, artefact, or professional, and minutes later you can be taller, prettier, or a fully-fledged member of the opposite sex. Heck, why not all three?

A popular trope in video-games and high fantasy, where often the only limit to these fantastical transformations is the inability to swap races, and sometimes not even then.

When used to change a character's sex, this is a form of Easy Sex Change. Not to be confused with Magic Plastic Surgery, which is when real plastic surgery techniques are portrayed as this.

Fan Works

 * A great number of The Legend of Zelda: Ocarina of Time fan works are based on Zelda's disguise being this, rather than simply an illusion spell of some kind.

Film

 * The Happily Ever After potion in Shrek 2 is able to transform Shrek, Fiona into humans, and Donkey into a stallion. Only lasts for a day, unless sealed with true-love's kiss.
 * What happens to Dragon under the effect of this potion anyway?

Tabletop Games

 * In Vampire: The Masquerade, this is but one of the many, many miraculous wonders the Tzimisce are capable of through their unique power of Vicissitude. Laughably, raising your Appearance score using the power is Difficulty 10 (in OWOD, Difficulty is what you have to roll to succeed; the game uses a ten-sided die, so...), and if you suffer Critical Failure you get uglier.
 * There are some things that even Vicissitude can't do—trying to change a Nosferatu's appearance is impossible.
 * Changes that make them prettier, anyway. Changes that make them uglier, or cosmetically status quo (don't move their appearance trait at all) stick, while improvements 'heal' painfully in minutes. Makes sense considering Clan weaknesses are a malevolent curse rather than a genetic quirk to be fixed.

Video Games

 * Once you craft a make-up table and mirror in Animal Crossing: New Horizons, you are free to alter your appearance in it at any time.
 * City of Heroes: Thanks to the Super Science Super Booster, heroes and villains can now easily change the size and shape of their bodies, even switch genders. Of course, in a world where there is a black market for magical artifacts and super science is used daily, this is pretty well Justified.
 * This is the in-universe excuse for Shepard's appearance if you change it between Mass Effect 1 and Mass Effect 2; s/he died in the interim and had to be completely rebuilt.
 * Star Wars The Old Republic has "Appearance Designer Kiosk's" that can provide this service, provided you have enough Cartel Coins.
 * World of Warcraft barbers can change your gender, hair, facial features, and skin colour.
 * Galathil from Skyrim offers this service for an affordable price down in The Ragged Flagon.
 * In the world of Elden Ring, one need only approach the Clouded Mirror Stand to change your age, gender, or any other cosmetic features of your character.