you can easily change font and swap x and o with these modified registry files (japanese style x and o) DOWNLOAD it worked on my psp (european 2.8 firmware) im pretty sure it works on other firmwares too.
1)copy modified registry files to root of the psp's memorystick (system.dreg , system.ireg)
2)Download tiff font hack installer and copy fonthack folder to psp's photo folderHERE
3)get fontmod folder to the root of memorystick and the font you like to use fontmod folder + some fonts
4)go to photo folder end highlight fonthack folder and press start you should see some action in 2 seconds if not then restard psp and try again :)
5)when fonthack is running press O and wait till white text appeas and press home
6) now you should have custom font and japanese style buttons
very ugly tutorial by: TaMs