This plugin works fine on single installations. I installed it on a multisite installation and it worked okay with the root domain but none of the subdomains could find their renamed login pages. The old login page URLs didn't work either.
I have quite a few multisite installations so if you want to contact me directly to work on resolving the issue, I'll be glad to help.
Use webmaster -at- sf-fandom -dot- com to contact me by email.