You just swap the casing I do believe. I know my friend's older brother once just bought one and put a few heavy rocks in the casing and they took it :/. Talk about idiots. But I think they do more checking now adays.
well we are just going to switch motherboards, so the case and hard drive will all stay the same.
im gonna use a blow dryer to melt the adhesive on the outside sticker so it will come off and the ill put it back when done and it will be like it was never opened.
i just want to hear from people who have done it so ill know what to expect.