This film really annoyed me. The crux of a What if? story is that the new universe must be manifestly different.
Nope. This isn't that, and those aren't the "rules."
It's manifestly an old and common writer's fantasy: what if someone could go back in time, or something, and "become Hemingway? (please, Gentle Reader, feel free to substitute a writer or musician you prefer, rather than sharing your criticisms of Hemingway with me. Life's too short)."
John Gardner did this one at least once, back in the 70s. Strictly within the sf genre there's the short story "Doing Lennon," by Gregory Benford.
There are always untoward and sometimes catastrophic consequences, because of course the protagonist's success is built upon fraud. But the focus is not on some "alternate history" bombast, but on the motivations and morals and eventual comeuppance of the imposter.