(Image: Fallen Angels by Edouard Cibot, 1833)
Can an all-powerful God change the past?
If so, would it be as if X instead of Y had happened, or the case that X had happened instead of Y?
If it's as if, and God knows the "original" past but the physical evidence and every mortal (or angelic) witness's memories tell a different story... then that's not really changing the past, it's God lying to creation.
The past can only be changed if the "original" past leaves no trace, not even in the mind of God.
But in that case... God can't know whether the past has been changed.
Ergo, God cannot be both all-powerful and all-knowing. Sort of a theological Gödel's incompleteness theorem.
At one time, I planned to become a preacher. Probably just as well I didn't.