Editing /etc/default/grub is the only way I know of to change GRUB that will survive update process
The package grub-customizer mentioned in previous post used to change the menuentry order by renaming files in /etc/grub.d/ but this package was dropped from Manjaro repositories because it caused many problems with broken, non-bootable GRUB updates
Grub conflicts with grub-customizer - #24 by cscs
grub-cusomizer is crap software. dont use it. it doesnt work well. it breaks things.if you must use it … then use it with some other
grub… however you do it … you are on your own.