FEAT to feat

is it possible keywords like " feat "," feat."," featuring "," pres "," pres."," presents "," star."," starring ",
" vs "," vs."," versus "," meets "," with "," and "," & " always in lower case.

BLACK EYED PEAS FEAT. MACY GRAY - Request.flac
to
BLACK EYED PEAS feat. MACY GRAY - Request.flac

now I use this

$regexp($upper(%artist%),'(?#From "The Artist" to "Artist")^(?i)(?:the|der|die|das)\s+',) - $caps(%title%)

Hello new user atlantic, your request looks like you have confused something, so be careful with the following proposal.

If you want to change the filename, then apply an action "format value" against the filename, with the following format string ...

$regexp(%_FILENAME%,'(?i)\b(feat.?|featuring|pres.?|presents|star.?|starring|vs.?|versus|meets|with|and|&)\b','\L$1')

... this will change the given keywords into lower case.

DD.20171111.1245.CET

Please note that just changing the case of a filename usually is not noted by the Windows OS. The filename stays the same.
You have to really change the letters somehow, like add an underscore at the end and remove it in the next step.

I cannot comfirm this.
The windows-explorer does not refresh its view if you just change a letter vom lower to upper but if you change the folder and go back or close the explorer an open again or just reboot Windows shows the changes.

Thx;
is it possible that keywords like ft or ft. change to feat

You can any character or string with a simple replace action or action-group.
There ios no need of a complicated regex-replacement.