In age of empires 3 is there a way to change the computers difficulty midway through a game???

In age of empires 3 is there a way to change the computers difficulty midway through a game? I have been playing AOE3 and realized that it would be really awesome if i could change the difficulty so that i could build a BEASTLY base without getting attacked (CPU character being in sandbox mode at the time of me building) Than when i was done if i could simply set them to expert again and fight them in a all out war? PLEASE PLEASE PLEASE HELP ME!!!!!