Yes, he has. Markiplier often does unique and entertaining segments, and this could be one of them. He likes to interact with different types of content related to his fan base, and reading fanfics, even the not - so - good ones, is a way to do that.
His friends like Wade and Bob could be main characters. They would be the ones who first notice the change and try to help him. They might have some really funny reactions and also help him come to terms with being a girl. Maybe there could also be a mysterious character who caused the transformation in the first place and they have to find this person to reverse it.
I don't think it's a true story. Such heist scenarios are often the creation of writers and storytellers to provide thrilling and adventurous experiences. There's no evidence to suggest it's based on reality.
Well, 'A Cinderella Story: Once Upon a Song' is directly associated with Disney. Disney is known for its fairytale-inspired content, and this is one of their films in that vein. It features the classic elements and magic that Disney is famous for.