I did some digging around in the game's files yesterday while troubleshooting and noticed a few things that may be of interest.
First, the game has an editor! Don't know how to use it, looked buggy (rendering artifacts out the wazoo) as all hell, and I got the impression you can't edit the existing single player with it. (Could be wrong though) It can be started by checking the corresponding option under Advanced Options in the launcher, and I think there is a command line parameter that can be used too... can't remember.
Second, as you noted, there are many ASCII files in the directory that can be edited to control some things. Of particular interest is the Ahkuilon.rvm file in the Modules directory. It has parameters and scripts in ASCII format for many elements of the single player campaign, and indeed seems to be the principle file governing the campaign.
Ahkuilon.rvm is an interesting file, though. Not only is it full of ASCII scripts, but it is also a PAK file! By opening the file in WinRAR (Probably other similar tools will work too.), you can extract a host of other script and resource files used in the campaign. Only problem is I doubt we have a tool at our disposal to repack changed files back into the module file. You might try placing modified files in a "Ahkuilon" folder within Modules to see if the game handles overrides or something.
Speaking of PAK files, there are a couple other files in the root directory that can be unpacked as well. I forget their extensions, but I believe their names were Resource(s?) and Imagery... or something like that. You might be able to repack these as a common file type, like zip or rar, and then change the extension, but I didn't look to actually see if that's what's going on here. Again, both files also have correspondingly named directories in the same directory, so maybe there is an override system in place.
Anyway, that's about it for my findings last night.