It shouldn't mess up anything, as far as I know, since it's the OS on your phone the betas are controlled and sent out by Samsung and not the carriers, plus as far as I know this year Samsung opened the beta for everybody on any carrier or unlocked, I haven't found anywhere in their announcement that says only certain carriers are allowed like in the past
I believe if the phone is the unlocked U1 model it shouldn't cause a problem. But your mileage may vary. I would keep your old SIM card just in case it's necessary to switch your phones CSC back to continue getting OTAs.
You will need to be Reinstated by a Beta Community manager, if you switch carriers when using the beta firmware you will not be able to access the Forum