Then just ./bootiso ./your.iso But it comes with this error out.
bootiso: Found non-hybrid image; inspecting image for boot capabilities…
find: ‘/usr/lib/syslinux’: No such file or directory
find: ‘/usr/lib/syslinux’: No such file or directory
find: ‘/usr/lib/syslinux’: No such file or directory
bootiso: Could not find a SYSLINUX bios folder containing c32 bios module files on this system. Exiting…
bootiso: See bootiso/install.md at master · jsamr/bootiso · GitHub
Note that after writing an ISO to a USB, you should in theory be able to just add your kickstart and custom grub files and test it that way. But you must not modify the ISO before hand using mkisofs.
The guide you posted about repacking an ISO is not the best way to do for Rocky Linux. If you want to repack an iso, considering using xorriso, with the correct options, to avoid damaging the iso.
If you’re wanting to do the kickstart and some custom grub file before writing to a USB, use pure xorriso.