Possible maybe, in theory, everything is possible.
Can you do it? Absolutely no.
Firmware is not on hdd, so in theory, you need flasher, you need keys, you need a lot of stuff, wich you dont have. Not really sure, but i think for the moment, nobody can downgrade ps4. Correct me if i'm wrong.
All u can do is wait for newer fw exploit, or look harder and try to find <4.05 console.