So Congress can change the meaning of the Constitution all by itself?
NOT
The courts have ruled that such persons are naturalized at birth, since Congress has no other power to confer citizenship, except via naturalization. Naturalization can be accomplished in ways other than the "live in the country awhile, apply individually, take a test and take the oath" manner. Sometimes masses of people are naturalized at once, when the US acquires new territory, such as when it purchased Alaska or acquired Hawaii. (In both cases mass naturalization did not occur right away, but did not wait on statehood either).
Bottom line, NBC means what it meant when the Constitution was written, since there have been no amendments changing the definition.
Congress changes the Constitution all the time. Unless and until the federal courts stop them, its the law of the land.
Congress has been defining natural born citizenship as including those born overseas since 1790.
“the children of citizens of the United States, that may be born beyond sea, or out of the limits of the United States, shall be considered as natural born citizens: Provided, That the right of citizenship shall not descend to persons whose fathers have never been resident in the United States.”
And note John McCain’s natural born citizen status despite being born in Panama (which no one disputes) is established by statute since Congress gets to say who’s a naturalized citizen and who’s a citizen at birth under the Immigration Code.
“under sections 301–309 of the Immigration and Nationality Act (restated in sections 1401–1409 of Title 8 of the United States Code), current U.S. law defines numerous other categories of individuals born abroad, as well as people born in most U.S. territories and possessions, as being “nationals and citizens of the United States at birth”.
http://en.wikipedia.org/wiki/Natural_born_citizen_of_the_United_States