$regexp('Mass Of Man - Unhappy (feat. Olivia Charlotte (feat. Bingx)','(.*?feat.*?) \(feat\.(.*)',$1 &$2)
Leads to Mass Of Man - Unhappy (feat. Olivia Charlotte & Bingx)
This also works for
Mass Of Man - Unhappy (feat. Olivia Charlotte (feat. Bingx (feat. Misc)
in a first step as it leads to Mass Of Man - Unhappy (feat. Olivia Charlotte & Bingx (feat. Misc)
so you simply run the action twice.
To get the first & into a comma: $regexp('Mass Of Man - Unhappy (feat. Olivia Charlotte & Bingx & Misc)','(.*?) & (.*)','$1, $2' )
Use the scripting commands in an action of the type "Format value" or Convert>Tag-Tag