Compilations at end?

[simoncn]

If all these tags are AlbumArtist rather than Artist, you should be able to do what you want by putting the following in your tag updates file:

@ALBUMARTIST=Frank Zappa & The Mothers Of Invention
+ALBUMARTISTSORT=Frank Zappa
@ALBUMARTIST=Frank Zappa, Captain Beefheart & The Mothers
+ALBUMARTISTSORT=Frank Zappa

If they are Artist tags, you can use:

@ARTIST=Frank Zappa & The Mothers Of Invention
+ARTISTSORT=Frank Zappa
@ARTIST=Frank Zappa, Captain Beefheart & The Mothers
+ARTISTSORT=Frank Zappa

In this latter case, you would also need to add ArtistSort to itemTags and add Artist.value.sort={ArtistSort} to tagValue.