Upgrading to 4.30 CFW is very easy nowadays, so is downgrading if you enable QA and especially if you use Rebug CFW. So basically, this is what you have to do:
1- Make NOR/NAND dump (optional):
Install latest version of multiMAN, plug in a FAT32 formatted USB flash drive into the right USB port, go to mmOS->Select any file->Open in HEX viewer->[SELECT]->[START]->DUMP LV2(NO)->DUMP LV1(NO)->DUMP FLASH(YES)
2- Install Rebug 4.30.2 from XMB:
Download Rebug 4.30.2 from Rebug's website, rename the PUP to PS3UPDAT.PUP and put it on your FAT32 formatted flash drive in PS3\UPDATE and go to System Update and update from storage device (or something like that). Make sure there's no original game disk in the drive and that you don't update from the Internet or else you would install OFW!
3- Install Rebug Toolbox:
Install Rebug Toolbox from Package Manager, launch it and enable QA under Utilities. This is to ensure easier and safer downgrading. You can also change System Mode to Rebug to spoof to 4.31, XMB Operation Mode to Retail and Debug Menu Type to CEX QA. This is to ensure you have the Retail menus instead of the Debug menus which you probably don't need.
Once on Rebug 4.30.2 and QA'd, you basically can swap between Rebug 4.30.2 and Rebug 3.55.4 by just installing them on top of each other from XMB. No need for the tedious downgrader pup and dehashing that you probably did when you downgraded from Rogero 4.21 to 3.55. You can even put both Rebug CFWs on the HDD and swap between the 2 (by installing one on top of the other directly from the HDD). For this to work, you need to turn System Update Debug to ON and put the PUPs (renamed to anything you want, even without the .PUP extension) in /dev_hdd0/updater/. Then you can swap between them by going to System Update then Update via Hard Disk.
Regarding your PSN Games, I'm afraid you're gonna have to resign them or get patches for 4.xx CFW. You can find those on ps3repack.
Regarding retail games, you also have to resign patched eboots or restore your original unpatched eboots and/or install the latest original unpatched updates.
CECHL 500GB: OFW 2.50 > OFW 2.76 > OFW 3.41 w/ dongle > OFW 3.55 > 3.55 kmeaw > Rebug 4.30.1 > Rebug 4.30.2
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Off to my summer vacation, might be AFK for a while... Happy Summer!