Updating a bootable iso via pCompress is quite simple:
Click on iso in ROX-Filer Filemanager - mounts as a folder in /media (or /mnt for older pups)
Copy folder just made in /media (or /mnt) to main / folder
Rename it to what you want (leave / at start & remove .iso)
Click on iso in ROX-Filer Filemanager again - unmounts iso & removes /media (or /mnt) folder
Replace adrv and/or fdrv , (and/or vmlinuz & zdrv) using same names as original pup
In ROX-Filer Filemanager, right-click on your newly edited folder & click pCompress
Select .iso (not .tar.gz) & make location filesystem & click create, then click ok
Soon, a new iso is produced. Can then delete folder made earlier.
(Use at own risk. Note - iso's produced by isomaster fail to boot on some PCs)
Note: Can use updatesfsf utility to edit sfs. See:viewtopic.php?p=129038#p129038