Lol, just lol is all I can say. ;/ Guys there is no method to downgrade PS4. Firmware is not only on HDD, but also on built-in memory. And there are stored info about firmware version required to boot. There is no way to install 4.05 on ANY higher firmware, doesn't matter what trick you use.
Really guys, $ony is not that stupid to allow that kind of thing in their current gen.