I wanted to create something like this, but unfortunately the way the files are structured
seem to make this very, very hard.
Just about every map and resource file would need to be recompiled (and you'd have to create a lot of custom "munge"
.bat and script files to do this), and the resulting download size of the mod would be huge even if it didn't include
any new models, textures etc. Though it might be possible to use RTPatch or a similar utility to make a "mod patch"
which is applied over your SWBF installation, thus minimising the download speed.
It seems like Pandemic had to structure the game's data like this in order to make it as memory-efficient
as possible for the console versions. Moddability was probably a very low priority,
Battlezone 2 (SWBF's engine was developed from this game) has a MUCH more straightforward data structure. All the data files are stored in straightforward archives, not "munged", and modified data files such as .ODFs just go in a directory
called "addon" and override the ones in the archives.
It would be nice if SWBF had a feature like this - maybe some way of getting the game to use the "assets" directory
included with the modding tools, instead of using the .LVL files.
Still, good luck to anyone trying with a mod like this! I've given up and am just experimenting with custom maps at the minute. I have successfully tried compiling one of the side .LVL files (for the Rebel Alliance) and replacing the original
game .LVL file with it - and the game ran OK. So it can certainly be done, but will be a lot of work!