Each new chapter of American history has a way of casting what came before it in a different light. So when the composer Philip Glass and the playwright Christopher Hampton decided to revive “Appomattox,” the opera about the Civil War that they wrote a decade ago, they found that the changing civil rights landscape cried out for a rewrite. “We were writing it in 2005 and 6,” Mr. Glass said in an interview. “But it never occurred to me that the Supreme Court would gut the Voting Rights Act.” Since the first version of “Appomattox” had its premiere in 2007 at the San Francisco Opera, many states have passed laws making it harder to vote, and, in 2013, the Supreme Court effectively struck down the heart of the Voting Rights Act of 1965. So Mr. Glass and Mr. Hampton significantly revised the opera and made voting rights a central theme. When the reimagined work has its premiere at the Kennedy Center here on Saturday, presented by the Washington National Opera, audiences will see how Mr. Glass, perhaps the most prominent American composer of his generation, weighs in on a pressing issue in the nation’s capital — where many of the scenes he is depicting took place and where, if history is any guide, there are likely to be policy makers and a Supreme Court justice or two in the audience.