Tangent: This basically does that. It doesn't work perfectly on hpmor, though - it swaps the pronouns just fine, but only some of the names, so you have to not only remember that Harry is now Harriet but also do that without being thrown off by the fact that Hermione is still Hermione but with male pronouns. That's patchable (eg, eg), but I don't know that it'd be worth the trouble.