Locked self out of server and now very embarrassed

I opened Mac OS X Server on my laptop to remotely admin another Mac OS X Server (the name of that machine is "receptacle").

I had already been sharing the boot volume for "receptacle" and decided to edit the permissions to only allow the "System Administrator (owner)" "Read & Write" access, setting both "Administrators (primary group)" and "Everyone Else" to "No Access" (as shown in the screenshot; don't ask me why I have a screenshot.)

Of course, "receptacle" promptly began behaving very unlike its former self. That is, I'm mostly locked out (I can ssh as root but not as a normal user. Remote admin using Mac OS X Server launches but is pretty much unresponsive. I can no longer edit the File Sharing details for "receptacle".)

I'm not in front of the machine so can't boot into single-user mode (was considering adapting these instructions). However, I will be in front of the machine inside of the next 24 hours.

Can someone please advise whether there is anything I can do remotely and/or what steps I should take when back in front of "receptacle"?

Thanks for considering.