Yes if you opted to not to remove extra stuff. But still you can prepare the file and let the flasher script include it in final image. That way it should fit even when not removing the extra stuff. You just can't modify it later (without reflashing initfs again). If extra stuff it removed (and it really is not so important and you can get it back from backup image or original firmware) then you can edit it directly in /mnt/initfs couple of times. With editing bootmenu.sh inplace (which is much larger) I think I did it like 5 times until I saw error and got the file truncated, bootmenu.conf is smaller so it should be better. I can no longer test this limit since I enlarged initfs partition and shrinked rootfs in some experiment and don't know how to get back to smaller size. I like bigger initfs partition but cannot test this 'initfs almost full' situation with n770 properly anymore.