kmoore, I'm really having trouble parsing your response.
I don't care that the headstamp is distinct, I (and I think the OP as well) care that it is not incorrect. The round I used as an example is an obscure military round for which commercial ammunition has not been produced for 60 or so years; it's highly unlikely anyone else is going to pick up a round thusly marked and be able to ID it, much less cram it in to some random firearm and fire it.
If I wanted to clean the headstamp, I could easily do that as well, though in a rimmed cartridge it could easily affect the headspace.
Regarding liability, I would think all the companies processing. 223 brass into .300 Blackout without remarking it have probably figured this out by now. Reloading and firing reloaded ammunition is basically an acceptance of personal liability as far as I can tell from the legal jargon on all the suppliers and manufacturers websites, I think it would be hard to pin liability on someone that reloads some rounds for a friend and does not represent them as commercially loaded ammunition.