Roms don't flash bootloader and other certain things, so... The rule is really, don't downgrade official firmware, ever. Once you flash 4.4.2 or higher, you cannot downgrade. Roms are not included, as they don't touch the bootloader. So yes, if you were on official 4.4.2 firmware, flashed a 4.4.4 custom rom, and want to flash 4.4.2 official firmware again.... That's fine. But if you flash 4.4.4 firmware with fastboot or RSDLite, that's it.... No going back to 4.4.2. Now, my disclaimer.... You SHOULD be OK. There's no guarantees in life, especially on phone flashing.... Anything can go horribly wrong anytime and doing anything. So do all this at your own peril. ?