giving the insta-kill feature to another weapon besides the pistol and make it upgradable.
just use the property editor in KotOR tool or another GFF editor to edit the properties of the .uti file of the item you want to have an instant kill.
its pretty easy really,
where you add a property for say a lightsaber in the uti editor (i.e Damage energy) i think there is a death option, anjd you set that to 100% chance of appearence. Otherwise just max out all the other stats, should kill anyone.