God is neither totally above the moral law, nor under it. Else He would be either a whimsical bogeyman, or a Saint Nick. But Scripture says that 'as the heavens are higher than the earth, so my ways are higher than yours.' The moral law derives from God's unchangeableness. God is the same, yesterday, today and forever. So He is neither suprarational, nor irrational. Human emotions can become irrational when they do not correspond anymore with reality. Emotions are in themselves a-rational. But God cannot be called a-rational, or a-moral, let alone immoral. Nor supramoral. God IS Love.
God transcends human rationality in His own infinite rationality. To put it simplistically, God's IQ is infinite, but that does not make Him suprarational, as if He were not somehow completely logical, but rather mystical. In His timeless and unconditional agape Love God is not unemotional either. With Him all things are in perfect harmony. And though He is supratemporal in His divinity, inhabiting eternity, in His actions He is involved with creation on a continuous basis. Yes, Hebrews 1.3 says that He upholds the universe by His power. By the way, if humans had IQ's of say six hundred million, their instrumentarium to deal with reality would still be very limited and indeed would still require hope and faith, and certainly love, to continue to live in creation.
To come back to the moral law. Calvin put it this way: "Deus legibus solutus est, sed non exlex." "God is free from laws, but He is not immoral." And I add that He is not supramoral either. That is, He is not absolutely above His own law, nor of course under it. Somehow moral laws, also in eternity, will be the reflection of His will and personality. And so we have seen that He allowed brothers and sisters to marry in ancient times, but never parents and children. Abraham married his half sister. Obviously, then, God can change laws. Lest you think I consider this a light matter; the Mosaic law stated that 'accursed is he that takes his sister into marriage.'