No act of congress can change the meaning of a constitutional term. They cannot call "Arms" "flowers" and remain compliant with the Second Amendment. When they freed the slaves, they didn't declare that they had been free all along, they passed a specific amendment to accomplish the task. Same thing when they made them citizens.
I am not having any of that "living constitution" crap, and neither should anyone else. It means what it originally meant until changed by Amendment.
Of course no act of Congress can change the words in the Constitution—only a constitutional amendment may do so. But that does not mean that we must interpret constitutional clauses as if the only laws applicable in the U.S. was the common law as understood in 1787. When the Constitution was written, filing false tax returns was not a crime under the laws of any state (there was no income tax), but sodomy was a felony in probably every state; today, the former is a federal felony and the latter is not a crime, if consensual, in any state (at least post-Lawrence). The original intent of the impeachment clause in the U.S. Constitution, which holds the President and other officers of the U.S. subject to impeachment for “high crimes and misdemeanors,” was to kick out (and make ineligible for future office) officers who commit serious crimes. The fact that changes in law result in that “high crimes” now inlude tax evasion and no longer include consensual sodomy does not mean that our political branches have changed what the phrase “high crimes” means; legislatures have merely adopted criminal statutes to fit what the people believe should be crimes nowadays and otherwise to reflect changes in our lives (no computer crimes were possible in 1787), and the acts included within the phrase “high crimes” has thus changed.
The phrase “natural-born citizen” meant “citizen at birth” in 1787, and it means the same today; the terms are synonymous (”birthright citizen” is yet another synonym). Who is a citizen at birth, though, has changed at Congress has legislated on the subject matter. Congress did not change the original understanding or definition of “natural-born citizen” when it legislated in 1790 to make the foreign-born children of U.S. citizens natural-born citizens, or when it subsequently legislated to declare under what circumstances persons born within U.S. territory were citizens at birth (with the answer being “always, so long as they are subject to the jurisdiction of the U.S.). Congress has not changed the meaning of “natural-born citizen”; it has merely changed the laws of the U.S., which is the piwer that Article I of the Constitution vests in Congress.