If God declared it to be morally permissible to kill one day, does that make it so?

First of all, He is the same God of yesterday, today and tommorrow. Second, He is a holy God. Always has been, always will be. In that he is holy, that means that His morals are pure and unchanging. He would not repeal the 10 commandments, as these are the moral fiber of what it is to be holy. These are the things that embody to humans the will and essence of God's will and His way of thinking. God is not a loser, but your mockery shall cause you to lose everything. Amen.