The Impossible Downgrade: Why You Can’t Take a PS4 from 9.00 to 5.05
chips on the PS4 motherboard to "dump" (copy) their current data to a PC. : Using software tools like PS4 Wee Tools PS4 Syscon Tools
you cannot downgrade a PS4 from a higher firmware (e.g., 10.01) to a lower firmware (e.g., 9.00) on a standard retail console.
As of right now,
If you are on a higher firmware (like 10.01), you are likely better off updating to the latest firmware and using the new PPPwn exploit rather than risking a hardware downgrade to 9.00.