Wall stud planing/sanding

I am working on replacing a uni-body fiberglass shower stall that was installed in when my house was built, with a 3 piece stackable stall. The problem I am running into is the bottom piece is a little thinker than the original uni-body stall and won't fit between the wall studs. It almost fits, but is extremely tight against the studs in a few spots, so it's not seating all the way. The wall is a second story, non load bearing wall. I want to know if planing or sanding about 1/4 inch off of the 2x4 wall studs would cause any structural problems down the road. There are only about 4 or 5 studs than need to be planed, or even sanded down so the new stall will fit properly. When it comes to putting up drywall I am simply going to install a 2x4 screwed directly into the existing stud creating a flush surface again. I can't remove the studs do to location and ceiling design so it has to be done in place. Any advice on this situation?
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