I've only seen screenshots of editing BCS tie-ins so I'm inclined to agree that the others are not editable. However, I've never seen anything from EA or any reviewers explicitly saying that. Yet, several people keep claiming that it's been confirmed...I'd just like to know where they are getting that information.
In fact, this article seems to imply that other bowls ARE editable (end of the paragraph just above the second picture). Granted, it's a few weeks old but that's why I'm wondering where it has been confirmed that ONLY BCS bowls can be edited.
http://ps3.ign.com/articles/116/1169273p1.html