oh, that is impossible. Unless you use a script which is too much of work to do. I've been doing cpp editing for quite a long time and I also had the idea of one shot "ONLY" LAW but I found out to be not possible.
But I think my Idea was ok? If a mission maker wants to add an extra LAW shell, it means that he does not want to follow the reality which is ok because I ain't gonna play his missions but for those who seeks reality, that public, private thing is fair to adopt.
scopeweapon="private"; means the "WEAPON" is not able to be picked up from dead bodies. I used this on my custom OICW since by the time the US gives its soldiers the OICW, I'm sure they also will include that gun user identification system thing which is still only used by the US LAW enforcement personel for testing (you know that the OICW is an expensive and powerful weapon....) the scopemagazine="public"; means that the "MAGAZINE" of the weapon is able to be picked up from dead bodies. scopeweapon="public" means the weapon is able to be picked up from dead bodies.
Now this is the only possible way to make an one shot LAW currently, and for ever,,, unless you change the game engines or what ever internal game files, what ever you call it.