1) copy the firmware 2.6 on a memory stick
2) copy the firmware 2.0 on a ANOTHER memory stick

3) put the memory fw 2.6 and update
4) At the Eula disclaimer remove the memory stick fw2.6
5)put the other memory and try to continue the downgrade
6) after reboot the psp and check if the PSP FW is on 2.0 or 2.6
7) If the FW is 2.0 ... downgrade it with the downgrader

it's that i will test tomorow

what do you think ?