There are several instances in Scripture where it reads as if God did change His mind. The one I can think of off-hand is Jonah and Ninevah: “And God saw their works, that they turned from their evil way; and God repented of the evil, that he had said that he would do unto them; and he did it not.” Jonah 3:10
God was going to destroy the people and Moses asked him to change his mind. And he did.
Likewise, God was going to destroy the entire scene, but Moses questioned him about the righteous people there and wherer he would save it for five people? Since only four righeious people were found, Lot and his wife and their two children, God did destroy it.