Warning: Be aware this PS3 CFW is still under development, and like all PlayStation 3 Custom Firmware should only be installed if you are aware of the risk of possibly bricking your console. Although not a requirement, ideally it should only be attempted if you have a backup of your PS3 NAND / NOR and a hardware flasher available.
To quote, roughly translated: Hi all, What better than to come back with this kind of news!
Our friend and SGK developer releases today the result of hard work. Indeed, in the shadow he worked to bring us a CFW with features interesting and not yet seen the new CFW 4.xx
The basis of this CFW is based on the REX Rebug CFW 4.21 which is the most stable and most successful of the moment. He added the Debug menu and Rebug Package Manager for our greatest pleasure.
Some files from firmware 4.30 which ensures compatibility for the latest keysets. So you can play your backups favorites without a patch or fix. 4.31 is a spoof includes access to PSN and avoid unintended updates.
Debug menu displayed in setting
Rebug package added
Implementation of parameters Rex 4.21.1 Rebug cfw
Lv1 Lv2 and recompiled
Patched Peek & Poke
Coldboot game replaced
Theme changed from dynamic watch dogs
More corrections ...
Testers and developers: consolehackdev; SGK_84
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shanerocks: You'll need a flasher, there is not free solution.
weedge1212: QA flagging is mostly for safety reasons, I like it mostly for the System Update debug, which allows you to store different CFWs on the PS3 HDD and you can switch between them faster that way, without the need of a flash drive.
jace2: It's better be safe then sorry, downgrading takes less than 10 minutes, there is no good reason for you to skip that, but since both CFWs are at same version, I'd say It's possible. Btw, why do you want to change CFW? For most users, there will be no difference between this, Ermac, Rogero and Rebug.