Having thought about it I decided to do it from the start and ignore any differences in sizes that might crop up, leaving them (if they appeared) to be explained later, and maybe the commands tweaked to get similar results.
So, the following is (I think) what I did ...... no, I did not take notes
..... that is too much to expect!
1 Extract, using Ark, pclinuxos-kde-minime-2012.12.iso to /<path>/pclinuxos-kde-minime-2012.12
and open the directory in Dolphin, with a terminal showing attached.
2. cd to /<path>/pclinuxos-kde-minime-2012.12
(if necessary); su to root
3. [root@XPS boot]# unsquashfs -d unsquash livecd.sqfs
4. Added a marker file to unsquash/home/guest/Desktop
as proof the loopimage was edited
Delete original livecd.sqfs
5. [root@XPS user]# mksquashfs unsquash livecd.sqfs -no-duplicates -noI
(those options might not be needed)
Delete the 'unsquash' directory (rm -rf unsquash)
6. Because I know nothing of other boot arrangements I used Grub as the boot manager when creating the ISO.
To do this I added into the existing 'boot' directory the followinggrub
directory containing menu.lst
(copied from my installed system)gfxmenu
So the boot directory then contains gfxmenu file & grub directory and the grub directory contains menu.lst and stage2_eltorito
The contents of the menu.lst are edited to this
color black/light-gray yellow/blue
kernel (cd)/isolinux/vmlinuz livecd=livecd root=/dev/rd/3 acpi=on vga=788 keyb=uk vmalloc=256M nokmsboot splash=verbose
7. [root@XPS user]# mkisofs -R -b boot/grub/stage2_eltorito -no-emul-boot -boot-load-size 4 -boot-info-table -o /<path>/test-iso.iso /<path/pclinuxos-kde-minime-2012.12/
The ISO booted (in VBox) and the file I added is visible on the guest Desktop.
The options I used in the commands are likely not the correct ones, but they suffice for the moment to give a bootable ISO whose loop image has been edited.
end_of I hope EDIT:-
Changing the mkiso command above to use Isolinux gives the following mkisofs -R -b isolinux/isolinux.bin -no-emul-boot -boot-load-size 4 -boot-info-table -o /<path>/test-iso.iso /<path/pclinuxos-kde-minime-2012.12/
A little bit easier than including the Grub files.
I will try a write up of this in Tips & Tricks and await corrections there to the procedure outlined