I was thinking about jailbreaking today and came to the idea of downgrading to iOS versions that are not currently signed by apple. Is it possible that in an IPSW file, there is an indicator that iTunes reads and recognizes the IPSW as a previous iOS version and does not allow a downgrade? What if these specific identifications were changed to those of lets say, iOS 8.3, which is still currently being signed. Would iTunes allow the downgrade of this unsigned IPSW, thinking it was the iOS 8.3 firmware file?