This whole process would not have been possible without the help of Thomas Schmitt, the very creator of xorriso.
The easiest way to add a file(s) to an official ISO is by using a program called
xorriso, which allows us to add files into ISO images via multisession. The command that worked for me was:
xorriso -indev Fedora-Workstation-Live-x86_64-31-1.9.iso \ -outdev test.iso \ -compliance no_emul_toc \ -map "$file_or_tree_on_disk" "$path_in_iso" \ -boot_image any replay
I will be wiring a full tutorial after I have ironed out the bugs with the Kickstart install.