Can a square be perfectly round and still be a square?
Great. Can God change his mind or not?
Look, you've basically got two choices here. One, you can defend gore3000's assertion that God's law is immutable, and thereby abandon any claim that God is omnipotent. Or, two, you can rescue God's omnipotence by admitting that God's law is not immutable, and that therefore gore3000 was wrong in his assertion. And if God's law can be changed by God, then the possibility exists that God could declare, say, murder to be kosher tomorrow. Whether or not we think it is likely or not, the possibility exists that God can do such a thing if He wishes. And then we either accept God's new law, or we do not. If we do not, then it seems to me that Junior was right, and morals exist apart from God somehow.
What a choice - agree with the evolutionist, or destroy one of the central tenets of Christianity. Talk about your rock-and-a-hard-place kind of thing. ;)