A while back I tried to create my own version of knoppix but couldn't do it. I have done a bit of research and found that I needed to use an ext2 file system instead of the ext3 file system that has become standard for most major distributions. I used tune2fs to convert my ext3 to an ext2 file system and it all worked fine. The process took over 4 hours on my dinky computer, but by following the instructions in the o'reilly book knoppix hacks, I was able to make an isoimage. I then used the tune2fs utility to revert back to ext3fs and everything seems to be working ok.
I am a bit leary of screwing around with my file system structure so the next time I think I will try a loop back file (mounted as a device). This should work ok but I can be sure only by trying.
In any case, I now know that I can create a custom knoppix disk. I suspect that the same basic process can be used to remaster other isolinux based live cd's.