The wiki gives instructions on modifying the ISO[1] and the last step is
to recreate the actual ISO file. I've got my Arch installers on USB
sticks, but is it absolutely necessary to do this?


Couldn't I just copy the root-image.fs.sfs to the appropriate directory
on my USB (/path/to/USB/device/arch/x86_64/root-image.fs.sfs) instead,
and regenerate the checksums?


[1]https://wiki.archlinux.org/index.php/Remastering_the_Install_ISO