Maybe someone can give you a better answer as I only play one league but, yes the game uses the same name file for all leagues as far as I know. So you'd want to change the name file when you switch to a different league. As far as I know, although I have no personal experience. Here is a thread about a nice little utility that eriqjaffe made to switch to different names:
http://www.ootpdevelopments.com/boar...light=Switcher
And you can download it in the Utilities area at the Download Center or at the link in the thread to eriqjaffe's site. Hope that helps you any.