I believe all install images are ISO9660 compliant.
Therefore the basic outline of how to modify a Debian image should give some idea of how to proceed.
As was stated before there is, or was last time I had a look at it, a remastering application for PCLOS. This might work but they use a hybrid package management system using .rpm packages but using their own script to use apt-get and synaptic (Debian tools for .deb packages). It might be worth taking a look at but I doubt it would work without some serious modification to the script(s).
I know Mandriva had such a thing around 2010 but can't seem to find any indication that it exists now. You could check their documentation. I think this is gone though. I think if it existed I would be able to find some mention of it on the Mageia forums. Can't do it. Could be searching incorrectly.
I know you can extract an ISO and edit it, rebuild it to the standard (ISO9660) and, with luck, have it boot correctly. Am not on my Mageia drive currently, haven't been for some time, too busy, so I can't check to see what packages are available for converting a file system to that standard. Should be something there or in the Mandriva repo though. They have to have one to build their own standard ISOs that you are trying to modify.