That is one issue with same flight number US-NRT-SEAsia.
You will get MQM of the distance between origin and destination. The extra due to layover will not be added.
If you break the layover it will reprice differently or ask for additional upgrade instrument.
Same with seat selection, you cannot select a seat for one leg and another for the next leg on these same flight number flights.
I would call DM line and implement HUCA. It has worked before and not worked before.
$5800 DTW MNL plus a upgrade instrument, ouch! CZ YYZ CAN MNL in J cabin was $4-4500 Cdn