I've had this conversation with someone before. God can be unchanging and still react differently to different stimuli. Let us take water as an example. If you gently put your hand in water, your hand will go through it easily and softly, with almost no resistance. However if you slap water at a very high speed your hand will be in great pain and you will feel a huge amount of resistance. This doesn't mean the water has changed. The water is still what it always was - it does not change it's properties. It is you the slapper who has changed and by changing you have discovered the other properties that water has.
Its an interesting concept, but I still have a problem.
Water is something that has multiple properties which by G-d would be a contradiction to His Oneness. Using your water analogy, imagine happiness as blue water. G-d is happy. G-d is infinite. So there is an infinite expanse of blue water. Where are you going to put the angry red water? Wherever you put it, will create a boundary for the blue water impinging on its infinity. Wherever you can say, this is happy and that's angry, you've detracted from the infinite nature of G-d.
Besides for that, your explanation would mean that G-d is simultaneously angry, sad, loving, happy, etc. just as water always maintains its properties (with its various effects being a result of different external stimuli not changing properties). You'll have to clarify how this is a more logical explanation.
Likewise God is who he is. He does not change. But we change - and because we change the way he reacts to us changes. But the same thing that made God angry 1000 years ago will make him angry today. The same thing that made God happy 1000 years ago will make him happy today.
"Made G-d angry" is a change of state from "happy" to "angry".
In fact when you come to think of it your first paragraph does not make sense. You could as well say that the fact that God one day did not decide to create the earth and the next day he decided to create it means he changed.
No we can't because time didn't exist before G-d created it. There is no reference point with which to place G-d's "decision" to create the earth.
You could also say that the fact that God did not give the ten commandments to Moses on the previous day but did on the day he gave them also means he changed. It is illogical.
No, G-d is always giving the same bounty. Its the lenses that changes the bounty. Sometimes the lenses turn it into 10 commandments and sometimes into food, but the bounty remains the same. How the lenses change according to an infinitely Simple Will, is - so far - mostly beyond me. But I don't expect to understand the process since the starting point is beyond my imagination.
