I understand that fully, but Yamaha could have allowed the current 'old' fuel maps to be flashed back on afterwards by creating an update that would overwrite the 'new' maps.Not necessarily accurate...
I work with various embedded devices, which generally use a some kind of flashing process to install software.
When you flash a device via USB, for example, you're not directly overwriting the flash chip. Rather your interacting with a bit of pre-installed software (often called a bootloader) which performs the actual flashing onto the chip.
Before commencing with the actual flash, that software could (and should) perform checks, e.g. the validity of the software being flashed, that its a newer version than what's already installed, or it could not allow anything to be flashed...
If the latter is the case, you might need to dismantle the flash chip from the board of the ecu and forcefully flash it using a high voltage on certain pins, or what ever other method the flash manufacturers describes, in order to overwrite the bootloader itself...
Anything is possible if you can bothered to actually do it.