As Ultra said, you can remove the valve screw rivet. Catch the edge of the rivet with a knife blade and carefully pry it out. Remove the valve screw and replace the o-ring with a Viton O-ring, then tap the rivet hole for a #8 screw, blow out the debris and then reinstall the valve screw. Screw it in and then install the set screw. I used a gas resistant sealant on the set screw just to be sure it did not leak.
If you decide to drill the rivet out, be very careful, the dril must be perfectly centered so you don't end up with and elongated hole.
Hope this is what you were looking for.