Messing with weapons.dat is fun. If you mess anything up you can easily delete the mod and go back to redo it. It's also silly fun to make conc blast only cost 1 ammo.
No. It simply changes the animation used when firing the gun. Unless that is what you meant.
If you want the character to fire from the shoulder you'll need to change the stance as well as the firing animation. This can be your first animation test. Tip: you don't need to use Dragon for this. Unless you make a new animation.