No, I believe you can forget programming into the game's executable files. What I am sure will be supported, is to:
- modify text files, changing loads of things,
- modifying unit textures & image files, effectively allowing you to create new 3D models and import them by replacing old ones.
- provide basic editors, like unit editor, battle field editor, provincial campaign editor, and historical battle.

I don't know if you get a map editor like the one in Civilization, but the main map can probably be modified a lot.