Hi djohnson,
There is no way to change an AppleID associated with a purchase. The AppleID used to purchase the item (whether it be music or apps) is forever tied to that item. However, when the box comes up asking for a password to update, you should be able to see the ID tied to the item in the same box where it is requesting the password.....
Hope this helps!
Also, the new iCloud address that is automatically assigned to all iCloud users does not create a second AppleID if your primary AppleID is an @me.com or @mac.com address. Not sure what happens if it is something else, but If it is an @me or @mac, if you try to sign onto iTunes with the iCloud address, it switches to the primary @me or @mac AppleID when the sign-on is processed. Just an FYI....
Cheers,
GB