Question

How did Lincolns policies on slavery change as the civil war continued

Answer 1

Lincolns originally said slavery should be preserved in its current colonies but shall not be expanded. 
That was the politically popular/convenient thing to say without losing the election. 

Lincoln wanted to keep the union together and if that meant keeping slaves in the South so be it. 

When the emancipation proclamation came to his desk, he re-examined the political climate and decided to do what was morally right despite political backlash.