I think this is an interesting but (apparently) subtle argument, so lets take it a step further for illustration purposes.
The US could repeal the first amendment, and explicitly make being a buddhist illegal, if enough congressmen got on board. There is a clear well known process for this, and in fact even precedent as previous amendments have been repealed. This does not make it incorrect to say 'freedom of religion is a inalienable right in the USA', because it is such today, as the law stands, the fact that congress has the power to change this doesn't make it a false statement...