its not too difficult to do if you have a good set of small, sharp, precision, numbered drill bits.
Ive done it on a few occasions in the past. My recommendation is to find a bit that matches, then go up one size (number), check to see if that will work. Drill thru, visually inspect. Repeat until you find the diameter what you want.
Remember, you can take metal off pretty easy, just a LOT harder to put it back if you go too much.
Finish off the exposed, shiny metal with your favorite cold bluing and youre done..
Dont turn the drill bits a high RPM. slow and steady is better, and tapping fluid is a big help with those tiny drill bits. let the tools do the work.
to clean up any burrs you will probably get coming out the back side, just get a drill bit 5 or 6 times larger. turn by hand on the hole to gently remove the burr and give the hole a very slight champher.