It took me a while to figure out eactly how to do this (probably as the option only arrived recently) so in case anyone else needs to do the same...

If you are creating a remaster and want to test it, you can use the fromhd cheatcode to load it up. I'm not sure (could anyone clarify it) exactly how much of my system it is using, for example I would be sure it is using the KNOPPIX/KNOPPIX (and that is all I have changed) but I would not be sure where it gets it's kernel from? I suspect that it comes from the cd.

Of course, any method you can use to boot knoppix can boot your remaster like this with the caveat of the kernel etc. But if you (like me) are doing a remaster from a cd, only booting that cd and using one partition to hold the remaster, you can just use knoppix fromhd=/dev/hdaN where N is the partition number containing the KNOPPIX directory without touching any bootloaders.