Yes, the replacement is shipped in new packaging, as if you bought it from the store. After speaking with a customer relations rep today, I was told that I have 14 days to exchange a defective, replacement. Now, the store can choose to do this exchange, but it is at their discretion. They could be negative, and say "NO!" But normally they help people, and will offer an exchange if problems are found on the replacement computer. You must first call Apple and explain the issue at hand, and they will give you a service ticket number, which contains all of the notes on the current problem, explaining to the tech to give you an exchange, or send it off to service.
In my situation, I have a flickering screen on my just replaced MBP 17". After reading up lots of posts and various forums of users who have this same problem, no solution was found. The only thing apple does is either replace the screen, or the logic board. I can go in and exchange, from what I was told, at that stores discretion, but I don't want another Nvidia chipset based Macbook Pro. I'm hoping those new units are released on the 27th, and hopefully contain an ATI chipset. If I'm blessed with that good news on the 27th, off to the apple store I will go, and see if I can get it exchanged. Problems you may face: 1) Paying a difference in price if there is a price drop (hopefully they are not that money hungry, but we do live in the United States, so don't be surprised) 2) Finding the right person to assist in the exchange process who won't fight tooth and nail with you to send it out for repair, and not exchange it. So my advice to you is to pick the most friendliest apple store and go there.
Please also, keep in mind, that replacement will be mailed to your home, possibly from China, like mine was.. but that 14 day window does begin when the customer relations rep places your order, not when you actually receive it... This is what I was told... from customer relations... Good luck!