My co-admin and I worked on this for quite a while (together and individually) and couldn't get spawn protection to work on a map-per-map basis even though we followed your example.  I decided to make a separate game profile for those maps that I wanted to use it on; but, even then, the mutator did not work properly.  Wish I had more time to play around with this, but I simply don't.  All's not lost, though, 'cause I stil have your excellent rifle for our Zark matches.  :)