google translated from Russian
All you need to run the firmware without a key is to throw aim_spu_module.self of their firmware and instead return the version from 4.25 OFW.
After that, you need to rebuild the firmware file, and can be installed on <= 3.55 console.
But I recommend that you try to do this to people with flasher.
It works, we tested but may not work for you because of improperly collected pup-file.
So either wait for someone to rebuild the firmware, or try to farm, good tools for that.
Another note that downgrade it to make a special firmware, and after replacing the file, you will not be able to rearrange this version of the firmware on the very same myself.
P.S. She has a firmware bug, so some games may not work.