Not quite what you're looking for but Pretty Face is a great "I'm not really trans but I have to be for flimsy excuse" manga.

It's about a guy who gets in an accident that puts him in a coma for a year and is so badly mangled he needs his whole face rebuilt. The doctor who saves him has no idea what he looked like so he builds him a face based on a photo of his crush that was in his pocket. As it turns out, his crush has a missing twin sister so he decides to impersonate her to keep his crush happy while he searches for her real sister.

While the MC never explicitly identifies as trans in the text, there's a bunch of supporting subtext for it. He slowly gets more and more used to being seen as a girl and isn't in the biggest rush to get his old face back even after he finds a photo of himself for the doctor to use as a reference.