RT-N66U interface failure and nvram

I upgraded an ASUS RT-N66U router, and it broke the user interface. The router has been a very good one, very reliable until now. Does anyone wonder why we all hate upgrading? Okay. Deep calming breath. I can no longer set the DNS server address in the DHCP tab; I can ssh to the router, and so set the DHCP DNS server value that way. Looks like

nvram set dhcp_dns1_x=192.168.19.1

There's a lesson in here somewhere.