This is coming straight from a solicitor not myself in regards to the Round 13 rule. Once a player signs a contract they are in the eyes of the law an employee of that club from the start date. Any break in that contract via the Round 13 rule would be regarded in the eyes of the law as a breach of contract. The round 13 rule is not a law in Australia and therefore is not a valid defense in a court of law if a club take the case to court. The cooling off period for any employment contract is 72hrs. So the NRL is just opening the door for legal action with the Round 13 rule.
So if DCE was to backflip which imo he won't the club has the option to take him and Manly to court and seek damages for breach of contract.