@Zaper8 The Peaceful rank could be on an automated timer that resets if said player kills another. Like, if Player 1 doesn't kill anyone for (x) ticks then they get the Peaceful rank, but if Player 1 kills someone the rank gets removed and the timer resets.
The staff wouldn't even have to play a role in this, it simply means that a player with the Peaceful rank isn't running around trying to kill players.
What about tp traping and tnt killing? there are ways to kill someone without it being tied to your name