I haven't done any mods I regret but the previous owner of my favorite hunting rifle electric pencilled his license number on the barrel. He did this to every rifle in his collection, I've owned a couple of them. He also drilled and tapped a commercial Oberndorf Mauser for a reciever sight. This is after he took off and filled the holes for the rear sight and ripped the sling swivel off the barrel. Oh well, it's still my favorite hunting rifle.