In an adaptation of any work, be it a TV series, a novel, or even a remake of another film, there are bound to be some changes made. Sometimes Age Lift is used, making a child character older, or an elderly character younger. Adaptation Distillation removes elements, and Pragmatic Adaptation changes the story altogether to fit the new medium.
This trope is one that more often than not is not intentional. This is the case where a character's general hairstyle is changed from one adaptation of the character to another.
You'll most likely find this trope pertaining to female characters, as Long Hair Is Feminine, and long hair is much more prone to change than the relatively uniform short hairstyles given to the majority of male characters. If they're doing a live-action adaptation they might also change the hair from practicality as some hairstyles are difficult or outright impossible to recreate in real life. This could also happen with animated adaptations, as limitations in animation technology (especially with CGI) could also play a factor.
This trope occurs when a character's hair length, texture, or style changes significantly between adaptations. Or, the character's hair never changes in the original version, but the adaptation version of the character does receive a hairstyle change.
An example of the first is a character having short hair in the original version but then getting long hair in adaptation, or maybe the reverse. An example of the second is a character with curly hair being adapted with straight hair. An example of the third would be a black character who originally sported an afro instead sporting sisterlocks. An example of the fourth would be a character who in an adaptation gets an Important Haircut when they never did in the original version.
Super-Trope to Adaptational Dye-Job, where the primary thing changed about a character is the color of their hair.
This trope is almost guaranteed to occur if a character receives a Race Lift or a Gender Flip. Often the result of Real Life Writes the Hairstyle, which can cause adaptations of characters to receive different hairstyles that either wouldn't be practical for actors in live-action, or difficult to animate in animation.
Adaptational Hairstyle Change has been suggested to play 2 roles. Click below to see other actors suggested for each role, and vote for who you think would play the role best.