Race Change & Argent Crusade

Q u o t e:
If race change my NE hunter to a human hunter in Cata do I lose all my status with the Argent Crusade quests? and when will I be able to race change? Couple of weeks after Cata?

Our Faction Change FAQ covers most of the questions you'd likely have.

http://us.blizzard.com/support/article.xml?locale=en_US&tag=FCFAQ

Of particular importance to your question is some of the notes towards the bottom of the page in red text.