If you don't mind me butting in here a bit :)
Let me try to tackle your logic bomb. So there has been no shortage of paradoxes that have been raised by combining various claimed properties of God, and so in discussions about God, at least in discussions where we can hope to get anywhere at all, there is usually an implicit premise:
"God can be understood (or at least partially understood) with Reason"
And so the major characteristics of God should really be qualified with this, for eg: God is as powerful as is possible by reason. God is as all knowing as is possible by reason. Without this qualification, the old unstoppable force vs immovable object will immediately make short work of any possible discussion of God.
Adding this qualification may be justified in a number of ways. In the first place as I said we can only possibly have discourse with this in place - and the reduced claims (making reason a limitation) are still meaningful claims. It is also possible that paradoxes like the immovable object and the unstoppable force are absurdities created by the nature of our cognition and so limiting God's characteristics to logic may not actually be a "limitation" but a removal of absurd/false constructs inherent in our cognition.
So anyway, if we accept the additional qualification, then it becomes quite clear that the paradox you're proposing is just a variant of the immovable force/unstoppable object. It is coherent with the reason-qualified version of omnipotence if I were to claim that God cannot change His mind because He has full knowledge of all possible situations and thus would already have a plan. I can also claim, again coherent with the reason-qualified version of omnipotence/omniscience, that God CAN change His mind when it is related to free-willed agents (assuming we are such), because the definition of free-will requires that God cannot determine the outcome of the willing (even with reason-qualified omnipotence), and so God can still react and "change His mind" when free-willed agents like us (presumably) choose different actions.
thanks for the contribution, it's an open floor here as far as I know. I'm not going to try regulate people's posts unless it is rude or trolling.