So I received a new SIM for my phone. It’s a TF64SIMC4 V2, exactly as the “old” one differing only in serial number. As expected, it bricked my phone when I installed it. (Note: That is normal, since cell phone companies register the SIM to their neworks. I knew it would happen. There’s reasons for it, which involved the companies doing things the cheapest possible way, but it’s lousy security.)
I sent an email to “Sr. Mgr. Kimberly Filardi” at 9:52AM, asking to proceed with the number change. In theory, I could probably use the online phone activation system (which has worked in the past), but I suspect that would zero out my existing airtime and service days.