I am afraid.there is not an easy way to roll back ePO once it upgraded successfully.
Still you can detach your DB.
Remove ePO 5.
Remove defauld DB and ateech previos one.
I am not sure if you export all your policies and settings and they will work with 4.6.6.Same for Agent to server communication keys as well.
But no worries.Run a syn task and add your all systems and deploy agents over exixting one.
have you made a backup of ePO 4.6.x before you upgraded it to 5.0? I see a little potential risk just detaching ePO 5 DB, removing ePO 5 and reinstalling ePO 4.6.x (latest patch) then attaching ePO 5 DB; if epo 5 db structure is not compatible with epo 4.6.x.
But this could work after all. Just felt this ought to be noted.