Regex replace help for multi-value fields

[LyricsLover]

You are looking for an action which appends
space(Performer)
to any entry in your PERFORMER tag which not already have any value in brackets, right?

If you want to

@Zapgok

filter out these files correctly,

you could press F3 and enter
NOT PERFORMER MATCHES \(
this would show you all tracks where the PERFORMER tag doesn't include an opening bracket

You can find more examples here:

Filter expressions

This topic collects useful Filter expressions If you have a useful filter expression, please post it here and give a short description of what it does. These filter expressions can be used with the Mp3tag filter [F3]. Please look at https://docs.mp3tag.de/filter for the documentation. Notes All filter keywords must be uppercase. All operations are case insensitive, for a workaround see this post.