All creation’s states do exist in mind of God as mind states. God however needs an indicator in which it points to current state of creation in God’s mind making a one to one map between the state of creation and related mind state. This indicator however is subject to change hence God’s mind which is contrary to the concept of changeless God.
You mean that there must be some thing in God’s mind that corresponds to each state of affairs in the world? And since the world changes, God changes?
Even if the first statement were true (and I do not concede that*), the changing in the world would not imply that the indicator corresponding to the change in the world would itself change. So it does not follow that God changes. This is because the one-one correspondence need not represent the temporal mode of creation as a temporal change of the indicator.
To illustrate: Assume a created substance x changes over time. You claim that the map must be one-one, so they must be some y in God that changes over time. But God’s knowledge of the change need not be some aspect that corresponds to x while it exists. There could be a set of “indicators” in God corresponding to x at t0, x at t1, x at t2, etc. (This would follow if we characterize x not as “x changing over time” but as “x at t0 to t2,” which I think a realist account of time will require.)
*This itself seems to assume an account of omniscience that is contrary to simplicity. God’s single eternal act of willing and knowing is a willing of his own goodness and a knowledge of his own nature. Since God is perfect, his willing of creation, though included in this simple act, is not necessary. So God has a single act of knowing, despite knowing many things. To say that creation’s states “exist in” God’s mind as distinct would imply that his knowledge is actually composite, which is false.
There exist only one future since creation is performed in one timeless act. Future however can be subject to change if it is enclosed to an agent who have free will which is contradictory.
There is only one future because there is only one actual world; that is known independent of concerns from natural theology. Future cannot itself be subject to change because it is merely potential and non-actual. (Qua future, that is, it is non-actual. But it is only the future
to us, and not to God, who is not in time.)
I don’t know what you mean by “enclosed to an agent.” Free will is one reason (and some might argue the only reason) that the future is contingent. But when I act freely I am not changing the future, which does not exist. I am actualizing the future of this particular possible world. What the freedom of my act means is that in some other possible world with a history identical to ours, I acted differently; a different possible world
could have been actual on the basis of my freedom. But I am not changing the future.