There doesn't seem to be a generally accepted concensus on this topic. Some have not cut theirs and are fine. Others, myself included, had tires very close to the pinch seem even on the smallest amount of up travel. I'm running 35" GY MTRs (actual diameter is 34.5")
After (ignore the red lens flare):
if you air down and disconnect, yes.
I'm running 315 duratracs on a 3.5 inch lift and have had no need to cut my pinch seam. When it flexes the rear tires seem to go backwards, not forward so it's all good in my land.
Stock, most definitely.
With lift, you may be able to get by without having it done if you just go for mild to moderate wheeling.
Yes, you would need to remove the rock rails before trimming the pinch seam. I don't see a way to get at it without doing so. Furthermore, with the rock rails off they're also much easier to trim. It was just a couple hour evolution for me doing it by myself.Did you remove the rubi rail to make the cuts?