Sorry about the late reply guys.
Pertaining to the statements: the AtmosFear engine is actually really forgiving, and it even gives you good bug returns when you screw up. The language is some sort of Java/C homology but it's oddly written [insert joke about everything being backwards in Russia]
I'm afraid to say that my windows computer literally blew up (complete with loud bang) and I've taken it away but the news isn't good so I'm not sure if I'll be able to do any more Modding with Cryostasis (unless I can get it going on Linux). I was lucky to be able to recover that little file off the harddrive
@Lazarus187: Have a look in the player definitions file for the head bob - I think I remember seeing it there, it's then referenced in camera.s after the player data is loaded in the movement block of the code.
@J9Masano: Swapping weapons out is as easy as changing reference numbers in the base definition files, although I couldn't seem to get any of the "unplayable" weapons working - there was one person who did but he didn't give much information on how this was done. By the looks of the files there should be about three weapons floating around that are used by AI characters but not the player, so the first person models might not be there. In saying that, I'd garner that Vivisector models might work in the game also.
Again: apologies for the late reply, and perhaps one day I'll get this game up and running again on something.