Perhaps I should of started off with this instead of the level changer tutorial, but adding level changers seemed more useful. Anyway, this guide as you have no doubt gathered is going to tell you how to adjust the most significant weapon paramaters. Its all self explanatory stuff really.
Class - This paramater defines how "good" the weapon is to NPCs. The higher the class, the more likely a NPC is to pick the weapon up. Example: the worst class for handguns is WP_PM, whereas the best class for handguns is WP_USP45.
Cost - Defines the price of the item at traders.
ammo_mag_size - Another obvious one, defines the amount of bullets each clip holds.
ammo_class - Defines the type of ammunition the weapon uses.
wm_size - How big the bullet hole is.
fire_dispersion_base - Effects the weapon accuracy. Lower numbers increase accuracy and higher numbers decrease it. Eg; more accurate 0.01, less accurate 0.1
misfire_probability - How often the weapon will jam.
condition_shot_dec - How fast the weapon deteriorates.
hit_power - Determines the weapons damage. Higher numbers increase damage.
rpm - Effects the weapons fire rate.
silencer_hit_power - Determines the firepower of the weapon with a silencer attached.
snd_ paramaters - These individual paramaters can be tweaked in conjunction with other changes in other files to reduce how much noise is made when you draw / reload / fire the weapon with a silencer attached. Eg; snd_silncer_shot = weapons\silencer4a, 0.338. The weapon is 33% of its maximum volume with a silencer attached.
scope_status - Options are 0, 1, 2
silencer_status - Options are 0, 1, 2
grenade_launcher_status - Options are 0, 1, 2
0 = no attachment allowed, 1 = always attached (non-removable), 2 = attachment can be attached and removed. Note you cant do daft things like attach a PSO-1 scope to a Makarov PM. The mesh doesn't have the bones so attempting to attach a scope will result in a CTD.
Ok! Well that covers the main paramaters within the weapon ltx files.