This a very simple app, just put the official 6.20 updater in (ms0/ef0 accordingly)PSP/GAME/UPDATE, and run the downgrader, this will reboot into the 6.20 "update", and allow you to downgrader to 6.20. Has been tested on 1k, 2k, 3k, and Go (added support for 07g/09g).
I will be releasing the source on May 29th.
v3.5 Download: http://www.mediafire.com/?i8ae1j3xdxpshwj
v3.1 Download: http://www.mediafire.com/?jfavewhvu85jrz2
v3 Download: http://www.mediafire.com/?hhvqimvthbtrvis
v2 Download: http://www.megaupload.com/?d=0VBRZ8ZN
v1 Download: http://www.megaupload.com/?d=ZYEU7KFI
v2: 09g/07g support added.
v3: added support for 6.39, added model printer
v3.1: Fixed idiot bug for 6.38 I created when adding 6.39
v3.5: If the 6.20 updater MD5 check fails, it will check if the update file is 6.35, allowing non 07g/09g to downgrade to 6.35, added source, removed a few debug printf's
If you have anything lower than an 07g place the 6.20 update in PSP/GAME/UPDATE.
If you have an 07g or an 09g, place the 6.35 update in PSP/GAME/UPDATE.
No screenshots added because it's only text (splash screen as pic1).
Important note: You run the application at your OWN risk. I am not held accountable if you fuck up your PSP.
Another important note: After you downgrade to 6.20, you will get a BSOD (saying that your system information is corrupted), this is OK, just click circle to reset your system information and you will be back to normal.
Final important note: It does indeed still support 6.35/6.31
6.35 update: http://www.psp-hacks.com/file/2036
6.20 update: http://www.psp-hacks.com/file/1855
6.20 Go: http://www.mediafire.com/?l96b6wm3b92dwzp