I’m not where I can look right now, but did you look at variable “BOOTLOADER”? Many variables are concatenated, sometimes you don’t want to change an entire path (as mentioned I am not where I can look right now, but if you change a whole path you may be changing more than you bargained for).
Just FYI, a Jetson in recovery mode is a device instead of a host. Your host runs a driver while flashing a recovery mode Jetson…this is through the driver package (a custom driver). Part of what that driver does is load software onto the Jetson which makes it capable of responding to flash commands. Even though the Jetson is now a device, it is still a computer of sorts…it still needs to boot, but it needs to boot to recovery mode operation. fastboot.bin is used to reach recovery mode, but is not installed permanently…this version of fastboot.bin goes away as soon as a flash operation is completed. There is a different stage which loads u-boot to eMMC, fastboot makes this possible. You don’t want to alter the script environment so far as fastboot.bin goes.