We have a number of verses that make the subject statement clear, God does not change. He is the SAME, yesterday, today, and forever. Therefore, ANY doctrine we develop that causes God's character to change or His authority to shift, is changing the Word of God. It doesn't mean we have done an evil, it means we have reached a conclusion that needs to be reworked out. Case in point... recently on this forum I was told that there is "more grace today" than there was before. But since "mercy" (grace and mercy are the same thing) is actually mentioned more times in the OT than grace/mercy is in the NT, how can that be? And how can that be when "mercy" is a character attribute of a God who is the same yesterday, today, and forever? I am not really looking for an answer on that... I am really making a statement from the question.
The story of Joseph is one that cries "grace" from start to finish. In fact, so much so was God's hand on Joseph that Joseph said to his brothers later, "You intended to harm me, but God intended it for good to accomplish what is now being done, the saving of many lives." God was with Joseph, showing him mercy through each ordeal that lead to Israel (the tribes) being saved from the famine... consider...
Had Joseph not had the dreams he did, he would not have upset his brothers. If his brothers did not become angry with him, he would not have been thrown into a pit. Had he not been thrown into a pit, they might not have seen the slave traders he was sold to. If he had not been sold into slavery he would not have been chosen by Potiphar to tend to his house. Had he not been a favorite of Potiphar, he would have been executed over false charges. If it weren't for the false charges, he wouldn't have been in prison to hear the dreams of his cellmates. Had he not interpreted those dreams correctly, Pharaoh would not have become aware of Joseph and Joseph would not have become the #2 in Egypt AND his family (all the tribes of Israel) would have perished in the famine. Grace saw Joseph to the point of being used to preserve God's promises... grace is all through that story and those who don't see it, sadly, don't understand grace!
So the next time somebody says that the law was for long ago and grace is only for today... just tell them that God doesn't change and let it go. They'll figure it out, eventually.