.Rez Editting Help

Hey I kinda new to this. So I was wondering if this is right if you take say the LAW model and swap it with an assault rifle model the result is a higher fire rate and recoil but no damage change? Also i was wondering when can you take the default m16a3 and swap it with an smg to achieve a higher fire rate or is this not possible because I have tried it my self and seem to have failed (the gun is invisible and cannot fire)