"When I say to the righteous he will surely live, and he so trusts in his righteousness that he commits iniquity, none of his righteous deeds will be remembered; but in that same iniquity of his which he has committed he will die. 14“But when I say to the wicked, ‘You will surely die,’ and he turns from his sin and practices justice and righteousness, 15if a wicked man restores a pledge, pays back what he has taken by robbery, walks by the statutes which ensure life without committing iniquity, he will surely live; he shall not die. 16“None of his sins that he has committed will be remembered against him. He has practiced justice and righteousness; he will surely live," (Ezekiel 33:13-16).
When God states "If you do this, then this will happen; if you do that, that that will happen," it does not mean He is ignorant of the future. It means that God is revealing the results of what will happen as a result of our various choices. This absolute knowledge by God is possible because He knows all things, including the future and all its options. By contrast, this is not possible with the god of open theism because god doesn't know the choices that will be made, so he cannot tell with certainly what will or will not happen.
In Ezekiel 33:13-16 God is simply laying out the options of what will happen when someone turns from their sin. Since God knows our time frame, and since we are creatures of choice, the Lord speaks to us in ways that we can understand relevant to our choices of repentance.
The open theist cannot claim that these verses mean God does not know the future. These verses are telling us what the legitimate options are, and they are expressing the reality of God's desire that we repent from our sins. Therefore, God is not changing His mind. He is revealing it.