Specifically, how did the Dred Scott decision change African-American civil liberties?

Taney became best known for writing the final majority opinion in Dred Scott v. Sanford, which said that all people of Africa descent, free or slave, were not Untied States citizens and therefore had no right to sue in federal court. In effect, this meant that congress had congress had no power to prevent the spread of slavery

Interpreting the results of his experiment : )