6.60 PRO-B9 and every other pro are temporary hacks (although 6.20 has a permanent patch, if you want it). When ever you cold boot (boot from a shut-down; not to be mistaken with sleep/standby mode), it'll boot into OFW. From there, you'll be able to boot into the hack by loading a homebrew called fast recovery. You'll be able to boot into OFW whenever you want.
If you're going to update, to a newer OFW (currently, there's nothing higher than 6.60 though), you don't have to uninstall because PRO doesn't over-write stuff on your flash, iirc. But if you want to uninstall, it doesn't take that long.