I suppose prevention is better than cure, but if you haven't been paying due attention to traffic already in the circuit when you cross those numbers, and there is a genuine risk of collision when you arrive at your turning point for the downwind leg, I would take any prompt action necessary to avoid the collision even if it risked flying temporarily the wrong way up the circuit, assuming, of course, that you immediately turn back after passing the other aircraft so as to minimise the risk to other aircraft in the circuit.