A long, long time ago I goofed in a very similar way, moving around the /tmp filesystem, so I ended with an unbootable system.
The way to solve it without reflashing is putting an OS in the external card.
Problem, to clone the OS to the external mmc, you need a running N810.
Solution, download bootable debian, and put it in a 1 GB partition of your external mmc. You'll find the old wiki page with download links here:
http://www.internettablettalk.com/wi...p?title=Debian
Once you have the card ready, you can switch to boot from mmc using flasher:
flasher-3.0 --set-root-device mmc
Now you'll be able to mount the flash root partition (/dev/mtdblock4) and fix it.
Permanent fix: clone OS to mmc and boot always from there. When something breaks, boot from flash and fix it. Bonus: you'll have much more space to install software.