I thought I remembered seeing a script that allowed xref’d scenes to be excluded from the material override but the search is turning up nothing (using a lot of different combos of xref, exclude, override, etc). Anyone remember a post like this?
It is possible, I think I teased showing a screengrab of it working, but didn’t show how to do it 
I’ll release a script for it at some point soon but there’s complication of what happens when you re-load the file and merging in.
Thanks Dave. Yeah, I saw a bunch of your posts in the search but nothing with a clear answer. Hopefully I can do a quick workaround…