I can't find an answer to this. When switching between different roms through recovery can I use their original zip files or should I re-download the rom i want to use?
You're good to use the recovery files to go back to ROMs you saved... just keep in mind that you will need to update apps, and you'll possibly want to update to a newer version of the ROM if you go a while between switching. I always make sure my ROM is stable and make a current nandroid backup of that particular ROM every time I switch and delete the older nandroid to keep everything as current as possible =)
Ok thanks for the replies. So wipe data, factory reset, then restore a back up of the rom I want, then reboot, update, and finally make another backup of the updated rom?
You won't have to wipe data and factory reset to restore a nandroid backup of a previous ROM... the only time you should need to wipe data/cache and factory reset is if you are installing a new ROM. I switch back and forth between ROMs stored as nandroid backups without mouting system or anything (and I switch pretty frequently) with no issues whatsoever.