Syntax error in rc.conf - system boots "read only"
I'm new to FreeBSD (about 3 evenings), having used Linux for a while. I'm far from advanced in the console, but not a beginner either. BSD is different from Linux though... Anyway, here's something I don't find an answer to in the FreeBSD Handbook:
I screwed up my rc.conf by leaving off a quote (gdm_enable=YES"). Now I can't boot entirely. After it encounters the syntax error it stops with a question about the location of the shell (I used default). I log in as root. I edit the rc.conf, but it fails when I attempt to save it, with the message that the file system is read only. I tried safe-mode and single-user. Same thing. In Linux I would boot with the install disk and mount the partition and edit the file. So I booted into the 'fixit' live file system on the install disk. It warns that I need to make symlinks to this and that, or my permissions will get messed up.
Before I dig this hole any deeper, please tell me the best way to fix my rc.conf.