first of all you'd need to work out if it actually is a cabotage issue. The ticket as a whole is not a domestic ticket... do the rules apply if just two segments are concerned (I don't actually no).
secondly. an agent simply looking at at the reservation, even putting in seat requests or special meals, is no guarantee. You'd need to actually ask them specifically if the ticket breaches cabotage, which they'd likely have to refer, and have them look at it. Even if head office says it's ok, there's no guarantee checkin will allow it.
If it does breach cabotage, there are potentially several points where you could be refused boarding, including Australia, Tokyo or Seoul. Entry into China could be difficult as you wouldn't technically have a valid onward ticket (if you had a visa... no problem, but TWOV requires an onward ticket)