I'm a canon nazi with FPS, but for me RPS is something completely different. The entire way I approach writing RPS is different, the way I get plot ideas, everything. Whereas with FPS, I'm inspired by canon events and mainly want to write stuff that fits in the cracks or shows another possible interpretation, with RPS, I have ideas completely divorced from any canon. Just, "oh, I want to write a fic about a guy who walks in to find his flatmate and his flatmate's girlfriend shagging on the sofa, and it's horribly awkward and becomes obvious that the guy has a thing for his flatmate" and then I use whichever of my RPS characters fit in that situation. (This is exactly a fic I wrote last night, btw.)

There's a lot of my RPS that I change the names on and shop around to get published. But I enjoy writing in fandom, the interaction between writer and audience, so I usually post it as RPS first. But even if I weren't, as I said, the actors I like tend to fit personalities that I prefer, so I'd be writing the same thing anyway, even if I called the guys different names from the beginning.