There's not a lot to say about these traps. No need to modify anything, they are mostly used in special situations or by longtime muskrat trappers who have lots of them from years past.
As for the pin inserted to hold guard versus no pin, that part is open for debate. Depending on the model - style of trap & guard along with where the muskrat is when trap goes off, it is possible for the guard to lift the rat's body enough for trap to miss a catch. I wouldn't consider that a common occurance but if the trap comes with a spring pin, I'd use it.
In the past I have had rats wrung off in deployed #1.5 victor coils due to the bar's design. When fully deployed it stops parallel to the trap's base frame in horizontal position. That doesn't put enough pressure on the rat to pin them in place... when they avoid drowning long enough to slide their foot away from spring (strong) side of trap to the weak side jaws and end of guard bar, there is still room to twist and spin.
The #1 longs with guard bars that fully deploy vertical to trap frame keep constant pressure on the catch and prevent spinning at the weak side jaws location. That would be old style victors, new style bridgers. The guard traps that deploy in towards the spring like old-style blake & lamb and new dukes pin the catch to strong side of trap. I've never had a loss when using either of those style guard traps in any make or model.
Hope that helps clarify a bit