The wiki gives instructions on modifying the ISO 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?