It is generally safe to do so.
Generally safe? Short of brute forcing in a misaligned drive (upside down or something like that) or one that is too thick, nothing can really go wrong. Apple lists the HDD as a user-replaceable part, so you're all set.
Is it generally okay/safe to replace a stock (250GB) HD in a macbook with a 500GB - 750GB HD with out changing anything else within it?