Hmm, assuming you got a cfw, go to the recovery menu, then to configuration and change "Free UMD region" to enabled.
btw can u find me that kinda table for the slim models? (2000)
On higher firmware there's option to change the region number and enable free udm region. Change the number to your UMD's region and enable it.
Changing the region code means changing your key0x100, which is unique to each PSP. If any byte is changed the key will be corrupted, only making your PSP worse.
So unless it can be made as an plugin, or else it wouldn't work.
tried all 0x0100, 0x0103 & 0x120 containing REGION, but no success. And my psp not corrupted & still running in good condition.
hope someone make MULTI REGION for PSP like MULTI REGION ON DVD.
br
RNC_EBM
Have fun losing the UMD.
Unless you have backup.