It's actually very easy. I was fortunate to be able to watch Walther craftsmen do it 30 years ago and have done my own ever since.
The modern ones they do large areas with an electric tool but its just as easy by hand. The principle is hammering/vibrating not drilling so if you want to do it by power you need a tool like a vibrating engraver rather than a dremel. There are also multiple head hand tools but I use a single spike such as a sharp fine- ish centre punch.
Use a small pin hammer to keep it under control and tap the punch lightly but fast in multiple strikes, you don't want to hold the punch too tight otherwise you get too many strikes on the same spot. The trick is to let the punch "float" so that it wanders over an area, the lighter the strike and more pointed the punch the finer the stippling, harder and more angled the point the stippling is then coarser. I do a carefull single line with a fine point to form the edge and then fill in the area.
Get a piece of hardwood and practice first, keep the punch sharp and experiment with the size of the point, with care its not only easy but very satisfying, I can do a grip in about an hour and the finish is as good or better than the factory ones, I then oil the finished grip.
Go for it! Have fun.
Robin
Walther KK500 Alutec expert special - Barnard .223 "wilde" in a Walther KK500 Alutec stock, mmm...tasty!! - Keppeler 6 mmBR with Walther grip and wood! I may be a Walther-phile?