Mostly, I was using it as a way to modify other start-up files in /etc/rc.d before the later boot-levels started. Perhaps it would make more sense to simply create new versions of the script and let a new module (or rootcopy) overwrite the script, but in many cases I was applying a source-patch to the scripts in rc.S so that slight changes (like bugfixes) to Porteus boot scripts would not be overwritten by my own (possibly inferior) scripts. I also made a bunch of changes to configuration files using patches before the services using them started-up.
I'm creating an appliance that uses IBM's NIM-on-Linux (AKA NIMOL) to make the back-up and restore of my employer's AIX systems easier. If I place porteus on the first partition of each of a handful of large USB boot drives, encrypt the next (much larger) partition, and copy my back-ups to the encrypted portion, I have a highly portable series of restore devices that can be booted on a lot
of common hardware. Porteus boots on a lot of more recent systems that Slax cannot boot, so I'm trying to convert my devices to Porteus. By making a module with my modifications that don't change or overwrite the files of the core modules, I found I could make an "embedded" O/S for these USB restore drives that would be relatively easy to maintain for my purposes.
If I ever get this thing properly documented, I'll try to post it to my blog and link the post on the forum. I need a few modules outside the core and I created a module of IBMs NIMOL scripts. Unfortunately, I cannot repost the NIMOL script module, as NIMOL is a propietary part of AIX, but I can post how I created that module, as well, and anyone with an AIX CD should be able to do it, too.