Byron,
To get a better fit for my hand, I have modified the Morini grips off my Walther GSP and 208s and the following is the method I used to blend the original stippling with the area of wood I had to remove. You cannot tell by looking at it, where it had been touched up.
I used a countersink bit like the kind you would chuck up in a drill and by pinching the bit on the shank with the thumb and index finger you drive the point down into the wood by snapping your wrist letting the weight of the tool dimple the surface. Once you get a rythym going you can cover a large area very quickly and it is surprising how much control you have over where the tool strikes. You can go over it as many times as you like till you get the look you want. For deeper impressions you would strike the wood with a little more gusto by putting more wrist into it. When finished, it looks just like the stippling you see on the expensive European target guns.
Hope that helps.
Tony