Originally Posted by SouthDakota
If its possible, no one I know has ever had it done successfully. They are designed to be programmed once and then never redone.
Its supposedly similar to the Dell/HP/etc. flash drives that you can get with some new computers. They have Windows on them and that's it, you cannot take it off or add to it without "hacking" the firmware (partially breaking the built-in software). Firmware is pretty much the most basic level of programming that there is, much "closer" to the hardware than an operating system, such as Windows.
I am not sure anyone has bothered hacking our key fobs yet. If its even possible, it'd probably cost more in software/computer parts/labor than simply going to the dealership and purchasing a new one.
To be honest, there'd be little motivation to do such a thing, other than to create a re-sale market for fobs.
The more common issue would be someone getting a blank fob and cloning your current fob to it - something that has been happening ever since cars have had keyless entry systems.
My alarm system on my old truck actually reported how many fobs were keyed to the system during each start-up. That way, if you went out to dinner and it started reporting a third fob was active, you'd know the valet cloned your fob while he had possession of your keys.
The great thing was, you could wipe all the fobs from the system and program a new set if you found there were more than there should be. The system would then re-scramble the codes and create an all new set before allowing you to add your proper remotes back in.
Personally, I think that information should be available in the UConnect settings with the opportunity to delete any extra fobs that have been added.
Of course, the way things are going, programming an extra fob is actually the hardest option for someone to access your vehicle.