AppleCare won't cover the new hard drive, or any damage to your Mac that could be correlated to you having upgraded the hard drive yourself, but your AppleCare isn't outright voided if you do it yourself.
AppleCare won't cover the new hard drive, or any damage to your Mac that could be correlated to you having upgraded the hard drive yourself, but your AppleCare isn't outright voided if you do it yourself.