I don't think there is a safe and proven method to put a PS3 with min version of 3.56 or higher on a 4.30 CFW (like Rogero 4.30 v2) yet. I think if you tried to go from 4.31 OFW to 4.30 OFW you might get stuck in factory service mode, too risky!!
I would wait for now, maybe an expert will appear with help. Sorry I'm not much help