If I change my Apple ID on my IPOD, will I lost my existing settings and game progress?

I linked two IPODs to the same apple id and have been using them that way for a few months. When I download something on one, and it shows up on the other. Each ipod seems to have its own game prefs stored locally, but we cannot play multi-player games because they share the same ID. If I change the ID on one of them, will I lose everything and have to start over?

Thanks.