N is declarer, wins a trick on which E has discarded, and leads to the next trick. Before playing to this trick E says he revoked on the previous trick, he has a card of the suit. Since the revoke is not established the trick is opened up, E substitutes a legal card, revoke card becomes a penalty card, others are allowed to change their cards, (not relevant to this question), N is still the winner of the trick.
Question: Is N obliged to lead the same card to the next trick as he had earlier or is he allowed to change his lead? If so under which law?
Would the answer be different if N was not the declarer but a defender?