I am trying to edit a bootable Linux ISO. I find that when I simply open the ISO and save it, that it becomes unusable on the target machine. The symptom is "Unable to read group information from the repositories This is a problem with the generation of your install tree.” (In other words the kickstart and some of the other files were read successfully). I also notice that the ISO itself changes - it gets slightly smaller and the "LBA" values change slightly.
I also see this error editing the Rhel6.x ISO images. Turning compress to 'none' keeps the ISO the same size, but same error when booting it. Only workaround for me was to use my Ubuntu Linux desktop and install "ISO Master" for free. It made edits and ISO works fine.
Same thing for me on RedHat 6.5. If I use mkisofs with the following parameters, it works Mkisofs.exe -V "RHEL_6.5 x86_64 Disc 1" -b isolinux/isolinux.bin -c isolinux/boot.cat -no-emul-boot -boot-load-size 4 -boot-info-table -R -J -T -o D:\LinuxISO.iso .
But ultraiso causes an error on the detection of the repository by anaconda once started. Mkisofs seems to add checksums or other in a sector that Anaconda uses ...
I use the latest ultraiso by removing packets to take with the limit of the trial version.