I've tried to use the chatting method, but it doesn't seem to change my sprite's mood.
His (Yes, I've given him a gender :3 ) mood seems pretty dictated by what Event occurs during his action. If he trips and bumps his head, he gets depressed. If he discovers some awesome mining area, he becomes elated.
I send out my sprite to work a lot, in hopes that he'll encounter a happy event and move on with his depression.