retcon

noun

1. a subsequent revision of an established story in film, TV, video games, or comics: In an awkward retcon of his origin story, the hero’s parents survived the attack but suffered complete memory loss.

verb (used with object) ret·con·ned, ret·con·ning

2. to later revise (an established element of a fictional story): The writers retconned the origin of her powers, newly attributing them to alien ancestry.