I have a sneaking suspicion that you modded the gamefiles themself, without creating a new 'game data' folder?
When you patched the game, your modifications were probably overwritten because those files had been updated.
Simplest way I see of correcting your problem is to simply download a ready-made mod to change the damage, and then to modify the weapons in that mod... This is what i've done and its much easier, rather than fidling around with the original files.
If you take my advice, I woudl recomend downloading this weapon mod:
James Blake's Weapon Revamp Mod, Stalker Downloads, Stalker Singleplayer
HOWEVER, if you want to use that mod then theres a bug in one of the files but it's easily corrected. Locate the trade_barman file in the new 'game data' folder and remove it (Otherwise it stops you from enterring the bar area).
Once you have that mod installed, have a play around with the weapon files (The ones in the 'game data' folder... don't unpack the main game files)
Hope that helped
I'm quite new to stalker aswell
