Don't tell me Tesla updates carrier settings as part of their base software. That's the sort of thing that should be pulled every time it changes, immediately, on its own. Either way, if you're in 3G-only territory, having it try to find nonexistent towers might p*** off AT&T, but it won't change your connectivity, because the towers aren't there in that band.
And the worst-case scenario for talking to LTE should be that it won't see new towers whose downlink is solely in bands that AT&T didn't previously configure for LTE, and if the tower asks for a band that it isn't expecting, the radio might refuse, but I would expect that to be handled in the same way as a device that doesn't support a band because of hardware limitations, i.e. the tower will assign a different band. So support might be degraded a bit, and you might have a higher rate of handover failures, but it shouldn't stop working, unless I'm misunderstanding something about the way LTE handshakes work. And if you aren't dealing with voice calls, a handover delay probably isn't a critical failure anyway.
So why is this update necessary again?