It's taken me far too long to figure it out but I've finally got it working.
To change Horne, Lena to Lena Horne or
Hawkins, Coleman With Manny Albam & His Orchestra to Coleman Hawkins With Manny Albam & His Orchestra
Field: ARTIST
Regular Expression: ^([\w]+),\s([\w]+)
Replace Matches with: $2 $1
I hope I didn't miss the answer in here somewhere. If there's an easier or better way please feel free to help.