Have a look at the trim functions $trim, $trimLeft, $trimRight to remove surrounding spaces.
Try this ... for only one artist name
$regexp(%ARTIST%,'([^;]+)\s([^;]+)','$2, $1')Try this ... for multiple artist names
$trimLeft($regexp(%ARTIST%,'([^;]+)(\s[^;]+)','$2, $1'))... or ...
$trimLeft($regexp(%ARTIST%,'([^;]+)\s([^;]+)',' $2, $1'))DD.20120630.1120.CEST