It's not that hard (except for the soldering part, you'll want to wait for the solderless clip to be released) if you know what you're doing.
You can't brick the console unless you're stupid. All you have to do is make a backup of the NOR and keep a copy of the untouched backup. If anything goes wrong you can flash that back.
Either way there are tutorials to downgrade via ProgSkeet, but unless you're good at soldering I would recommend waiting for the solderless clip.
PS3 Slim CECH-3004A 160GB
PS2 Slim SCPH-70004 - FMCB 1.8b