BINGO! As previously stated, all three connectors on the chassis are the same. So modifying the control box power connector to be a keyed 2 pin does not prevent the 3 pin 5V sensor connector from being plugged into the 24V control box connector. In fact keying won't prevent the sensor from being plugged into the wrong spot.
That's interesting stuff, but not applicable since (a) the system is not using XLR connectors (the connectors look very similar hence the picture but about 1/3 to 1/4 the size) and (b) keying won't help or prevent anything.
I said it "it looks like that connector". It is not that exact connector. It is not an XLR connector as shown tin the example picture. The connectors I am dealing with are only 1/4" in diameter, an XLR is about 3 times that large.