Talked with my law buddy last night about the OP's original question. Like PBP, he could not recall an actual case where a legal firearm, reguardless of the modifications, was ever actually used to convict someone in a justifiable shooting case.
So if you shave your trigger to make your gun shoot easier, or put fancy grips on the gun, so long as you stay legal (Both state and Federal law) you should not have a problem. But if you are really concerned with this, then contact a good lawyer and ask him or her.
I tend to think that in a case of justifiable homicide, other factors would be considered before they got around to the modification you might have made to your gun or ammo.
Inside Every Bright Idea Is The 50% Probability Of A Disaster Waiting To Happen.