There is no need to clear A first if you're going to fill it with something else immediately anyway.
Good catch! I'll clear it out.
If the 'Bootloader Signature Byte' has "0xA5", that indicates that the device has a bootloader, and the device will jump to the bootloader after any reset. If the 'Bootloader Signature Byte' has any other value, that means the device either does not have a bootloader or that the bootloader has been disabled.