This is one of the reasons that I always fly with my Style PS Leatherman. TSA carry-on friendly and the wire-cutters on the pliers make quick work of the steel cable that holds the keys together. I've been cutting the keys apart on my National rentals for the last two years and never had anyone say anything upon return. One of the employees at one point actually told me that it happens frequently. I just leave the extra key in one of my suitcase pockets, and the tag in the console, and pile them all together in the middle tray when I drop the vehicle.
https://www.leatherman.com/style-ps-25.html