OH MY GOD. I CANNOT TAKE THIS ANYMORE. After 25 messages and three days, two problems that any reasonable person would have solved in about five minutes remain unsolved.
Nobody ever accused me of being reasonable. :)
Walk up to the Pi. Unplug it. Take it to a usable HDMI display. Plug it in. Fix any (possible but unlikely) issues caused by powering it down hard. Reconfigure the display subsystem for the new monitor. Fix the network issue. Take it back to where it goes. Plug it back in.
In our defense, we were trying to fix things possibly related to our local network, but we didn't have a conveniently accessible HDMI monitor there. Ergo the chicken and egg. However I did not know about editing the file by moving the microSD card to another computer entirely, as Jeff Galinant suggested.