(1) Whenever the claim or defense asserted in the amended pleading arose out of the conduct, transaction, or occurrence set forth or attempted to be set forth in the original pleading, the amendment relates back to the date of the original pleading.

(2) An amendment changing the party against whom a claim is asserted relates back if the condition of paragraph (1) is satisfied and, within the period provided by law for commencing the action against him, the party to be brought in by amendment (a) has received such notice of the institution of the action that he will not be prejudiced in maintaining his defense on the merits, and (b) knew or should have known that, but for a mistake concerning the identity of the proper party, the action would have been brought against him.

(3) The delivery or mailing of process to the attorney general of the Commonwealth, or an agency or officer who would have been a proper defendant if named, satisfies the requirement of paragraph (2) with respect to the Commonwealth or any agency or officer thereof to be brought into the action as a defendant.