So I want to make an action where everything after the first comma in the artist's field gets added to the title field and the last comma gets tuned to a "&"
For example:
Title: Only
Artists: Nicki Minaj, Lil Wayne, Drake, Chris Brown
After the action
Title: Only (feat. Lil Wayne, Drake & Chris Brown)
Try an action of the type "Guess value" (import tag fields)
Source:$regexp('%title%==%artist%','(.*)==(.*?),(.*)',$1 (feat.$3)==$2)
Target format string: %title%==%artist%