Paste the following line into your setuplevel.fpi (files\langaugebank\english\gamebank\mygame):
Quote: ":always,haveweap=eai\g36:headshotdamage=34"
Then just put such a line for every weapon that's in the game, that should adjust the headshotdamage, in haveweap you write the path to the weapon (without gamecore\guns\) and in headshotdamage the wanted damage.
The condition "haveweap" is only available in PG / PB, so, you have to use one of them.
Also, I didn't test it, so I can't guarantee that it actually works, but it should.
-Doomster