I don't know the specific file format for save games and other misc. data. However, I do know that save games are by default saved in a pretty well compressed format, so looking at the saves won't do you a lot of good. In debug mode though, there is an option to save a game in a non-compressed format. That should be much easier to hex-edit. Press F3 to get into debug mode, go into the save box, and press dump (or whatever) instead of save. That will give you the uncompressed version.
EDIT: Oh the unit stat themselves. Completely misread that. IIRC, currently the stats are hard coded into the program, so you would need to hex-edit the exe itself, a VERY tough problem to tackle. Also IIRC, getting a more modular system that is more friendly to modding is very low on the dev's priority list right now.