This mod from Bartimaeus makes it so the mechanic can upgrade all weapons and armor.
S.T.A.L.K.E.R. : Clear Sky : CS Technican Upgrades Everything Upgrade-able 1.0
(Note: The file, (stalkers_upgarde_info.txt), is spelled correctly. Do not change it, otherwise it will not work. Developers mispelled it, and that's the right path)
You may use this without my permission, whether to release another mod, or for your own personal use, such as making it so that ALL mechanics can upgrade everything. No credits are needed.
Simply place the folder in your directory, (default is C:Program FilesDeep SilverS.T.A.L.K.E.R. - Clear Sky for PC, not sure for Mac, or if Clear Sky even works on Mac, considering how horribly buggy this piece of garbage is, (which I love, :P)), and the Clear Sky mechanic, (Gray), should have everything able to be upgraded, (all armor, and all weapons that are normally able to be upgraded).
Credits: Gamedata Unpacker for helping me get the right file, & thingumeefish from the S.T.A.L.K.E.R. Files site for messing up his mod, which motivated me to fix it. However, I did not use any of his files, so no copy infringment was included in the making of this mod, :P