Kydex is quite easy to remold a bit, assuming you have the proper supplies. Kydex, when heated, turns to the consistency of a wet towel. The best way to work it is to get a heat gun (not a hair dryer or something like it, but a true heat gun), wrap a bit of tape around the part of the gun that has to fit (Kydex will shrink slightly when cooled, so a bit of extra width with the tape balances it out), heat the area with gentle back-and-forth motions, and when it starts to sag shove the gun in and let it cool. If you don't have access to a heat gun then a stove burner can do, but you have to be careful of burning the kydex and your fingers. Its also a lot less precise than a heat gun. I've remolded several of my kydex holsters; from enlarging a PPK/s holster to fit a PPK, to enlarging a Safariland 226 holster to fit the slightly larger than RS WE226. Keep in mind Kydex can only stretch so far, so if its too large of a modification it may not be possible.
Source - my grandfather invented the Kydex holster.