If I buy TC3 and register it under a new username is that fine? Or will that confuse CMP and ruin old 'gliderboy' content I'd have from my old username?
If you purchase a new game and register it with a different name it is no different than someone else doing it. You will get a new kuid number though so it could get confusing when you make your own maps and try to mix the content between the two different games. It would be seen as not your content by one game.