Your all over the place here. Bottom line, if God says do it or God does it is not a sin, so you are using the word murder wrongly in this context.
I don’t even understand your 3rd trimester argument; but I will say that a Christian battlefield surgeon can triage without committing a sin.
You don’t understand that the Holy Spirit is God and God does not change. The Holy Spirit is a counseler, he is an advisor, a gift of God. This has nothing to do with change and everything to do with your limits and mine. You need a relationship with God and one reason that you do is to have God in your life through the Holy Spirit.
So you're saying that what is evil is evil because God says it is evil? Then from whence our inalienable rights? If God can say at one point that killing helpless babies is an abomination and say at another point that killing helpless babies is a good and righteous act, what is the true value of that baby? It is dependent upon how God feels about it at that moment, therefore its right to life is not inalienable. I guess we can throw out that supposedly Judeo-Christian sentiment "We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable rights, that among these are Life, Liberty and the pursuit of Happiness."