FWIW
USSS code names are assigned by White House Communications Agency - it’s a joint military unit.
https://en.wikipedia.org/wiki/White_House_Communications_Agency
Yeah, but they’re not going to give a president a code name without their approval.
My understanding is the WHCA picks a letter, then provides a list of nouns starting with that letter to the principal and they choose one from a list. Hussein chose Renegade from the R-list.