I mean, the “legal area” of a fan edit is the same regardless of the source (film, TV, radio, book, comic, podcast, whatever) - there may be an argument for fair use, but overall, it’s a violation of copyright law.

As for the concept itself, I know that someone once tried to edit the Thrawn Trilogy comics to fit with the prequels (this was pre-ST), but I don’t think it was ever finished, and I don’t know of anyone who’s edited audio in the way you’re suggesting. It’s an intriguing idea!