The first problem is that I have to edit the metadata myself for various reasons. To keep the edited data from changing with the refresh, I usually lock the item, but the lock doesn't seem to work on the film cover. After re-scanning, it will still return to the original screen shot as the cover.
Second, the auto-generated assembly plug-in can't be locked either. I have two sets of the same movie with different resolutions. I set up two assemblies and locked the items, but after re-scanning, they all fit together in one assemblage.