I am pretty sure that the in game text for death attack can be PoV live edited so that those who aren't assassins can't observe the differences.
If this is too complex - please just give them "brutal attack" or whatever - and make their "death attack" a cooldown ability instead of something that is already really finicky to use.
I'm tired of hearing about "interesting fighting styles" in game and I am not even playing an assassin, jfc