Your request sounds like a question from the FAQ area, but here is a proposal ...
Filter: ARTIST MATCHES ",*The$"Filter: "$right(%ARTIST%,4)" IS " The"Filter: "$right(%ARTIST%,5)" IS ",The"Action "Format Value" ... or ... Convert "Tag - Tag"Field: TAGFIELDFormatstring:'The '$regexp(%ARTIST%,', *The$',)From: Artist,TheFrom: Artist,TheTo: The ArtistAction "Format Value" ... or ... Convert "Tag - Tag"Field: TAGFIELDFormatstring:'The '$cutRight(%ARTIST%,5)From: Artist,TheTo: The ArtistTAGFIELD can be any tag-field of your wish,...can be also pseudo field _FILENAME ...for example ...Action "Format Value" ... or ... Convert "Tag - Tag"Field: _FILENAMEFormatstring:'The '$cutRight(%ARTIST%,5)' - '%TITLE%