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No, you need to have firmware version 3.55 to install 4.31 CFW.
If you are not on 3.55, then you need a hardware flasher to downgrade.
Yes below version 3.55 is hackable
Here is 4.30 CFW, enjoy but you have to be on 3.55 to install it and backup NOR/NAND.
This forum software is better