You can't do that.
i tried it. there is this sticker on the seam where the PS2 is opened up (security seal sticker thingie) once you take that off it says void void void on it. And they check that when you go to return it. I thought i was slick and just ended up w/ a ps2 that i was hoping nothing broke on because i couldn't return it either.
I don't know about every store. but i used Circuit City.
my .02cents.
don't try it unless you are ready to keep the new ps2 you buy.