As long as you don't overwrite the rom with a NAND restore you can always reset your c3100 and boot into linux single user mode (b + d held down until login prompt comes up). To reset, remove power + battery for 60 seconds (maybe less, but 60 seconds works for me).
I had to do this myself several times during the OpenBSD install, and when my CF card caused the OpenBSD booter to not work (due to the linux boot process, supposedly).
You are safe... worst comes to worst you can always get into single user mode. Of course, if you run the OpenBSD installer, you will lose the contents of your hard drive, but if you don't care about that (don't need the japanese applications), then go ahead. There are replacements available to restore your c3100, but obviously not all applications will be restored.