Your reasoning is flawed. When you say God cannot change his mind, you must be talking about some biblical passage or event, or certainly some episode within the history of the universe. God’s mind, as theologians have put forth for centuries, is an instantaneous act. What God thinks happens at the same moment. There is no passage of time between. Why? Because time, and space, and the whole universe exists within God, not the other way around. In fact, time does not even exist outside of human experience. And even our experience of time is seriously flawed—we can’t even look at an object at the exact moment it is there, for the distance between us and the object dictates when we see it.
An omnipotent God can do anything he wants, while we are stuck in place and floating in “time”. So you are looking at God through a foggy lens, and believing yourself to be brilliantly clear. There is a time to create and a time to destroy. These times are not a change in the mind of God, but a change in the weakness of creation.
Furthermore, the will, ours and God’s, has two qualities—it acts and it allows. What you see as a change in the mind of God (therefore no God can exist—the actual point you are trying to make) when you see contradictions in scripture is actually God acting upon his creation and then allowing things to happen because of the freedom he gives to this creation.
This is greater and deeper than rocket science. This is why you, and mostly everyone on this website, cannot grasp it. Indeed, you spit out such understanding of God because it does not fit into your agenda—i.e., “I am so much smarter than any believer because I think on my own…and I will never listen to some religious mumbo jumbo…and I can’t see God so he must not be there…and on and on and on and on…”