Sure...
1.) But, you say that the grip is...too large !?
2.) Then you say that you want to "file" it !?
These two comments do not go together !
1.) If the grip is smaller than your hand - Yes, filing, grinding, sanding, restippling is done all the time. See below, my FAS6004. I used a high speed grinder, and some sand paper to reshape the grip on this gun. I removed wood in several places until my hand was comfortable holding the gun. I then took my little electric pensile, and restippled the areas that I removed wood from. Some areas I did not add stippling, I left it smooth. I still need to oil it, haven't done that yet.
2.) I both removed wood, AND added filler (epoxy) to my Ocelot grip (below). Some areas were too small, some areas were not comfortable. Mainly the middle finger area, under the trigger guard. I just removed the finish on the area of the middle finger area, then added an epoxy filler to make the surface more even with the rest of my fingers, grip diameter wise. You can't see the amount of material that I "removed". but it was a lot ! Especially on the "wing" where the heal of the palm rests on the left side of the grip. It's now about 1/2 the height that it once was. I also removed a fair amount of material at the bottom of my hand area, and at mi index, or trigger finger area, so that my index finger was more comfortable while on the trigger. I painted it with automotive "trunk" paint.
NOTE - I could...have used a wood filler, then restained and cleared the grip, but I like the roughness of the trunk paint. It adds overall grip.
THEN...there's my rifle grip that I molded to fit...MY...hand. It's a plastic grip that's a very simple shape. I wanted it to "fill" my hand. I have some "Marine" epoxy that allows a "fitting" like this to be done. I added the epoxy, then wetted my hand, then gripped the gun as if I were ready to shoot. After I was done, I found I needed to change it a little. I removed some of the epoxy, recoated it (see the two colors of epoxy), then placed my hand again, only in a slightly different position and gripped it like I was ready to shoot. Then...just let the epoxy cure. So now, every time that I put my hand on the grip, it goes into place the same...every time. I had the trunk paint from the Ocelot work, so I painted this grip with it too.
I actually did two of these rifle grips. One for my RTI Prophet Compact, and one for my Impact.
So again, yes, you can do a lot if you want to. I think that there are others on this site that have also modified their grips to better fit their hands.
It's better to fit the grip to the hand, rather than modify the hand to fit the grip !!!
Mike