Hello
You can decrypt CAS with working key( insert working key on slot) then edit short ISN and save then write eeprom back read again and decrypt to confirm changes.
If you are using hexprog after you read CAS data you need to remove BDM cable and connect key coil and insert key on that for decrypting, once ISN is decrypted and saved then connect BDM cable back to write to CAS.
For mode details you can contact our support if any doubts.