Board Thread:Skyrim/@comment-122.53.34.224-20161024000517/@comment-24524076-20161024003100

If you're playing on PC, look into console commands. Otherwise, SORRY! You're not going to see the Black Star on that profile unless you revert the save to before making that choice.

In other words, just like any other Daedric quest where you have a choice, there is no way to reverse it without cheating or losing progress.