Is it possible to use the values in a tag field as they appear BEFORE pressing the Lookup button? For example, let’s say I want to preserve the song title for tracks that have “Prod. by” credits in them (this is mainly a SoundCloud rap thing). I tried writing this script but it doesn’t seem to be working:
$if($rsearch(%title%,[Pp][Rr][Oo][Dd]. |[Pp][Rr][Oo][Dd] ),$unset(title))
I think Picard is searching the value of %title% after looking it up.
You cannot access the value of the original tag in the script. But if all you want is to have the value as it is already in the file and not use the new value provided by the lookup then you can unset the tag with $unset(tagname)
That’s too bad, being able to manipulate pre-lookup values would be a nice feature to have. If I unset title then every release I tag is going to use the original title values, even when I want them changed. I may go back to my original plan of using the per-track “producer” tag, but I took a look at some other releases and I felt the tags were wrong compared to my liner notes.
What might work is writing a tagging script that (before matching to musicbrainz) copies the title tag to a _temporary tag (e.g. %_original_title%) and then using that tag in another tagging script. I can try to write something later if you can’t figure it out 
I tried doing that all in the same script, are you sure it’s possible? I think it still takes the changed values, even if you make a hidden tag.
You could run one script manually on the untagged files (left side) first, which stores the tags in separate variables. Then in the actual automatically run tagger script you use those variables.
That’s how I understood @RandomMushroom128’s idea.