First ask upstream if it's okay to use "Lubuntu" instead of "ubuntu" in grub and nvram entries.

Then figure out a way to do that. AFAIK adding "--bootloader-id=Lubuntu" option in the 'grub-install' command(during installation) should do the job. Still I will check grub documentation once as I already have to go through it for theming grub.

Also need to make sure that the name is not restored to ubuntu after a grub update. Maybe add a script somewhere which notes if grub is updated and automatically runs the "grub-install' with the above option.