I don't think it's possible to make a easy way to mod the actual map, buut i will next week be looking into making it possible to edit and create your own countries, cultures, provinces and easter egg nations and saving them, that save file should be possible to be shared to others if you keep the name and location as the same.
I will also look into making the start of the game more customizable to get more varied games. one example is adding more countries provinces and letting you choose exactly what countries should be divided