I wonder if it's possible without re-registering?
I'd guess that it can't be done within the same registration. I bumped into the name issue when changing from MaxFixit to FineTunedMac. I don't recall all of the specifics but I do remember that, once you have a name registered, it sticks.
I don't think that's unusual. When I wanted to change my user name at a financial site, it required a re-registration.
Edited by ryck (10/13/19 10:43 AM)
iMac (Retina 5K, 27", 2017), 3.4 GHz Intel Core i5, 8GB RAM, 2400 MHz DDR4
OS Mojave 10.14.6
Canon MX710 Printer
Epson Perfection V500 Photo Scanner
Time Machine on 1TB LaCie USB-C
Carbon Copy Clone on 500GB OWC Mercury OTG Pro