Basically you can/should stick with the 5.5120. Once that bootloader is in your internal memory it can only ever be up, not, downgraded (unless you're a gambler AND really DO understand what you're doing).
You cannot "backup" your bootloader although you could "save" the system file to your desktop but that doesn't mean you can roll back to it.
As has been said, playing with bootloaders is dangerous so if you don't know what you're doing, forget it!
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