Reflashing is not the only solution I think. There should be "safe mode" -like something. Maybe R&D mode can do it for you. Even if it does not, you can boot another OS or chroot to your N900 -which I dont know how to do, btw- and repair your broken files.

on Desktop GNU/Linux, even if you mess up your boot manager, or something critical for system, you can still log-in to your system for rescue/repair using a LiveCD.