I can almost always lucid dream, but I’ve never been able to turn into not-me. No issues with flying (except the damn power lines in the way), sexy-time-on-demand, using doorways as portals to wherever I want to go, etc, but if I try to become not-me, I wake up. Can’t say I’ve ever tried to become a cow, though.
Possibly influenced by movies and games, I'm not-me in my dreams all the time. I've been all kinds of people, animals, aliens, non-corporeal entities etc, but as soon as I realize it's happening, not-me instantly becomes me.