Apple gives you instructions on their support site for how to do it. Yes: absolutely, replacing RAM and hard drives will not void your warranty.Then again, is it possible to do on the new macbook pro's without voiding the warranty? Can someone please answer?
I have the last MBP with a replaceable battery ( which I've never once swapped out), and replacing a hard drive is ridiculously easy on that. For the current ones, you have to take out 10 screws to get at the RAM or HD, which is a bit more of a pain in the ass, but, you know, how often are you going to do it?