So, I think this is even less complicated than I anticipated. Try replacing $copy(artist,artists) with $copymerge(artist,artists) and see if that does the trick.
Yes, that seems to be working great.
I had tried some other aproaches myself, but couldn't get them to work.
(overlooking the copymerge command completely)
So thanx again.
You must be having some use for it yourself too? Predecting that this could be desireable?
Perhaps add it to the script on wikia?
edit:
Running an album through Picard a second time will add artist entries to the 'display artist' tag.
That should normally be avoidable by adding display artist to the 'preserve tags' list, but as we know, that feature currently is broken...
edit2:
It see that 'preserve tags' does work for 'display artist', but you need to enter it as DISPLAYARTIST.
Is there a particular reason why you are using capitals in the script?
edit3:
I'm gonna test some more before adding more comments to this thread.
'preserving' seems to work for some albums, but not for some others? Weird. (but it could be an id3/vorbis thing)