just as a quick update:
you can edit the MapSizeDefs.xml in steamapps/[...]/DLC/EXP2_Crusade/Game and then delete the .bin files in [...]/EXP2_Crusade (Core.bin,GC3.bin,Options.bin/Particles.bin) and start GalCiv3, it then creates new bin files and takes changes in the game XML files.
If you want to play a larger multiplayer map you can edit the small-configuration(for example) and overwrite the data with the insane one and be able to play an insane map in multiplayer. (just don`t overwrite the InternalName part)
Note: changes to the game directory are not recommended and can cause bugs and errors.
Same can be done for factions with the FactionDefs.xml
Kind regards