I agree that Lincoln's views on slavery changed very little during the war. But he did share the racist views of his society and culture and that did not change too much either, during the war. However, unlike most of his fellow white citizens he did not, and never did, let his prejudice control him or his reasoning. His ideal, and favored way of dealing with the issue of what to do with the freed slaves was always separation, by colonizing them out of the country. But the almost universal uninterest in it did not paralyze him, into doing nothing at all. He favored emancipation in spite of its process not being as perfect as he would have preferred.
Lincoln himself, confessed that like most others, he did not control events as much as events controlled him. For instance, according to all that he said about slavery and emancipation, indicated that he did not want to get too far ahead of public opinion(North and South) concerning emancipation(i.e., it was coming, but timing was all important, but the perceived inability of his administration to successfully conclude the war, forced him to implement Emancipation, while public opinion was still generally opposed to it. Events forced Lincoln to balance the dangers of losing the war against the dangers of a too precipitate action on emancipation, i.e., he had come to the conclusion that the war could not be won solely on the issue of Reunion. Emancipation was needed and would come, but, the necessities of the war itself dictated when and where it would occur.
I think perhaps his friendship with Frederick Douglass was starting to change his ideas about race but unfortunately he died before it could go anywhere but then again....it might have not changed at all. We'll never know.
I have read many books on Lincoln my first in 1980And my last about six months ago a fascinating individual he was probably one of the most politically astute individuals I have ever read. Now what does this have to do with slavery you have to get into the mind of Lincoln and understand everything he did in the end help free the slaves but he did it in such a political manner that the average person of those times didn't know they were being pushed morally into the right decisions they believed it was militarily conducive to the war and it probably was but politically it was a masterpiece of insight and intelligence . The more I read of this man the more I respect with all the learned man in his cabinet he with a third-grade education walked right over them. Now that was a true Renaissance man.