Excellent!!! I booted to the beta 7 firmware USB stick, chose "Repair" --> "4 - Restore the Id firmware" --> "Try to preserve settings and Library?" and answered "n". The repair process did its thing. When I rebooted, all the settings and libraries were cleaned out, but this time, I had totally new network UUID's! I tried it again, and got a totally different set of UUID's. Hooray!
Now when I choose the "77 - Revert to default settings (HDMI, no library)", it reverts me to whatever set of UUID's I had after I flashed the firmware and told it to reset the settings, not the duplicate ones that existed before. Also good! This is what I would want and expect.
I did notice that the library Access Key got reset to the old "LBaaDO" in the restore-firmware-without-preserving-settings process. I am not sure if this is good or not (haven't played it out in my head yet), but in any case, it is easy enough to change through the Id GUI if it gives me problems.
Thank you so much for your help!