While there are several PS3 OFW Methods and some older games that work on PS3 OFW 4.81 without a second console on Custom Firmware, it's time to reveal the final method to running PlayStation 3 game backups on 4.81. NO CFW/ODE/another bs.
Be careful, there is a very high PSN ban risk. Already I lost few IDPS while online by testing this method. If you get banned on undowngradable console you got ban forever. Prefer to stay at 4.70 or to play offline.
This method I found few months later I decided to publish.