YES you can downgrade to OS4.0.1, but firmware that is 05.14.02 NO.
Operatiing System (OS) and Firmwars(Baseband) are two different things. you can play around with OS but once firmware(baseband)upgraded to 05.14.02, it can not be change as of NOW.
I am sorry but that is correct you can not use your phone until there is a new tool become available on internet.