Okay, so there's this kind of old yaoi manga called Chintsubu, where these guys were in a car crash and somehow, from the force of the crash, instead of dying, their souls got stuck in each other's penises. So after the crash they have to deal with suddenly having sentient dicks that talk and have personalities, sometimes a little different from what their normal personality is like.

Maybe when the Starkiller Base was collapsing Kylo and Hux got brained with a beam or something and that caused the switch- I don't really care how it happened. I just think the premise would be great.