No idea about the
Additional Tagging plug-in, but I was able to put this set of actions together for
Mp3tag (
https://www.mp3tag.de/en/):

I've included these below so you can copy and paste them if needed:
1. Turn the separate
Artist values into a single string we can work with:
2. If there are multiple artists, store the second and subsequent
Artist names in a
Guest Artist tag:
$IfGreater($StrChr(%Artist%,|),0,$regexp(%Artist%,(.*?)\|(.*),$2),)
3. Separate the single
Guest Artist tag into multiple tags (for which Mp3tag uses the
\\ delimiter)
$replace(%Guest Artist%,|,\\)
4. Update the
Artist tag to keep only the first Artist tag value:
$regexp(%Artist%,(.*?)\|(.*),$1)
NotesThis doesn't do any text matching for '(featuring XYZ)' etc. in your artist names.
It just separates out existing multiple value tags, which is how I've interpreted your request.
I've used a single pipe character
| as the temporary delimiter.
If you have artist names that use that character, you'll have to do them separately - I can't imagine there would be many.
I did limited testing on this, so run it on a small test batch before unleashing it on all 200,00 tracks in one go.
But you have all of your tracks backed up anyway, right? Right?!
