Because God is pure act He DOES now whatever he "wants" to do, or whatever "pleases" him.
I put those words in quotes because "want" which still suggests "lack" cannot rightly be applied to God. And neither can "please, since God has no appetites to be pleased.
What is left, though, is "will." More colloquially we can phrase the proposition as "God does whatever He chooses."
Now, to choose the evil, or to choose what is contrary to what one is is not REALLY choosing, but failing to choose. Humans fail to choose, because we are fallen and the effects of our fall include weakness in knowing what is good and weakness in conforming our knowing to our choosing.
But God possesses all power. SO he does not have the weakness of intellect and will that we have.
Therefore he only "wants" what is in accord with His nature as God and only what is Good.
Therefore it is impossible for God to change or to lie ( or to WANT to change or to lie) because the first is not in accord with His nature and the second is also an evil.
So God CAN do whatever He wants. That, however is not the same as saying God can do anything one could imagine.
So examination of the "trick question" can lead to useful thought about the nature of God, of will, of desire, of want, of choosing, and of reason.
That's a good way of stating it. Thanks. I still think y'all were basically saying the same thing, but that's just me. :o)