I couldn't say how to do this dynamically in game, but if it's something as straightforward as your example like just upping the damage, I would just edit the damage value of the base 10mm pistols you want to change in the geck. Every offspring of that gun will reflect those changes.
I am referring to multiple entries in the GECK, not ingame.
For Instance, I am working in the GECK with FOOK2 weapons, and wish to change the damage variable of the Beretta 92F, the vanilla 10mm pistol, the chinese pistol, and the Glock 18C, all at the same time, so that I dont have to go through and change each variable individually, as it would save time to do all of them simultaneously.
I am trying to change more than just those 4, and more than just the damage variable, but the example I presented should illustrate what I am trying to accomplish.