There's really not that much pressure on the fitting (limited to the "springiness" of the compressed rubber bellows), so the inner set screw should not be excessively torqued.
The set screws are a softer metal than the shaft, so the inner set screw deforms a bit when tightened. Accordingly, PSS says NOT to re-use the inner set screw.
The outer set screw not only holds the inner one in place, but it is also designed to replace the inner set screw after the inner screw has been removed. For that to happen, the outer set screw should not be torqued very much at all, otherwise it will also deform and not be able to be used as a replacement inner set screw.
PSS sells replacement set screws.
Before you start tapping and fussing with the fitting and set screws I would put in a call the the folks at PSS. I had some questions for them about a year ago concerning my PSS
shaft seal. They were very approachable, informative, and helpful. They might be able to give you some useful suggestions.
Good luck!
Bob