loctite sells a product that fills in the head of a screw (phillips or hex, something other than flat head). Don't know thet product number as I haven't used it in years.
It forms a hard waxie substance that removes easily enough for warranties but not so easy that you will do it by accident.
And unless they wish to purchase same color and type it is hard to replicate and also leaves behind a slightly waxy residue that keeps "look alike" material from sticking.
Call loctite up and give them your situation and they will tell you what to use.
thanks
Michael T.
"If you don't stand for something, chances are, you'll fall for anything!"