Formally Disproving Divine Command Theory

[Mystic]

Then you have yourself a new Holy Book by definition. If God tells you how to live, then that stops being Deism and it starts being Theism i.e. the belief that God has revealed some nature about himself.

If God tells you in words, then yes, you are right. But if it is morality as we know it and that's God voice in creation, then Deism originally had the position, that we know God's will via morality and rationality, and we don't need him to reveal words.