However, if the universe objects do not have the same internal IDs in both the .unv and the .unx, just changing the universe won't work as you'll have to map the two (I've run into this issue....)
Also, the RESTful Web Services SDK provides the functionality to change the universe of the individual data providers in a Webi report as well as getting the information you would need to re-map any objects that don't match.
-Dell