This is the crux of what you say, imo.
God sees God acting in time with me. We have three stages presented to us. (1) On the outside of time stage1 is God. (2) On the other foreknown stage2 we have God and me. (3) On the realtime stage3 we have God and me.
Stage1 God foresees Stage2 God and me and then the foreseen becomes a Stage3 real God and me. (This makes my head hurt...lol.)
On a human level, let's say that on Friday night I envision myself making a bank deposit on Saturday morning(Stage1). I see myself walking into the bank, going up to the teller, handing over the transaction papers, leaving the bank (stage3). On Saturday morning I make it real by actually doing as above (stage3).
When we place the dilemma of Exodus in this schema, we really receive no relief from this simple foreknowledge perspective. Since God's foreknowledge is perfect in this view, God would still know that God is making an offer to Moses that God has no intention of following through on.
We should look at the Hezekiah passage where God tells Hezekiah that he will die. Why didn't he say, "you need to plead with me or else you will die?"
That is the key, 'intention'. God has every intention of carrying out what He said.
He, however responds to how man handles that warning!
Thus, even God's warning to Moses is real, and Moses handling it is real, God knows the outcome, but since Moses is free, the outcome could have been different.
That Moses chose to act in a way that moved God to 'repent' does not negate what God intended to do when He warned Moses.
God intended to destroy Ninevah and would have unless they had not repented.
That God knew what they would do, does not lessen or negate God's intention when He warns them, because in real time He is giving them a choice and will Himself act on that choice.
Nothing God says in time is 'untrue', God knows the outcome of the choice that man makes and what He will do also, but the choice has to be made first in time, hence the dynamic nature of the system.
God is seeing how His interaction with mankind 'plays out' and that is what is 'foreknown', but not a foregone conclusion until God sees it happen in time as real.
Why would God say that?
The desire to pray to God for longer life came from Hezekiah and God responded to that plea.
Did God always know that would happen? Ofcourse, but the decision to do so was Hezekiah's and God responded to it.
David gets told in 1Sam.23 that if he stayed in Keliah the men of the city would deliver him up.
There was no 'if' in the message.
David overthrew the 'Eternal Decree' by leaving the city and the 'predication' did not come true.
Had David disregarded the predication and stayed in the city, it would have happened and history would have been different.
Davids response to God's prophecy was as real as was the propecy itself.