Last sentence first, you are right, you are expressing weak human logic, not what the Word of God says. Following your logic, God set man up as the fall guy, then committed the first capital punishment on the earth, since He is all knowing.
There are a number of times in the Bible God changes things, especially His operating instructions to man. In the dietary commands alone, which are simple to track, which do we follow? Do we only eat salads and vegetables, or the meat of any animal we can catch, or only selected meats that are clean, or all things as long as we receive them with thanksgiving. All are Scriptural. God changes His instructions and in order to be in His will, man needs to follow the instructions God has in operation at that time.
What you're doing is confusing the immutable nature and character of God with His ability to change whatever and whenever He wants. He is sovereign which gives Him the privilege to change things. However, He always was, is and will be God. He will fulfill each and every promise He makes and has made. He will live up to His covenants with Israel because He is the one who made the covenants and they are irrevocable. But to say God has never changed anything is to be blind to what's in His Book.
Who knows what that mystery involves? God has no obligation to spell out to us all the details of ANY of the mysteries He allows us to apprehend however fractionally with whatever fraction of our finite brains.
I can accept that God changed His mind without understanding how to mesh that thoroughly with His unchangeableness. But He defines all that. He IS all that. Not me in my finiteness.
But if you wish to put yourself on God's level and tell Him what He can and cannot do and can and cannot be--by all means--help yourself. Please excuse me if I don't stand too close to you in a thunder storm.