Hi,
I've got a crazy itinerary soon on oneworld (booked via OTA, Malaysia Airlines ticketed).
Outbound is PNH to DFW (via KUL, NRT)
I'm returning DFW to RGN (via HKG, KUL - DFWHKG with AA, HKGKUL with Cathay, KULRGN with Malaysia)

I'm needing to get to RGN asap and have just dicovered a Dragonair flight (also oneworld) HKGRGN direct (ie not via KUL) that gets me in many hours earlier than my booked ticket.

If I book a redemption seat on this dragonair flight, will the agent in DFW allow me to check my bag only as far as HKG? Or will they let me check through to RGN but on the dragonair flight?

I suspect both will be "no" and I'll have to waste several hours travelling, but thought I'd ask and see if anyone had any experience of such situations.

You are correct. If you want to do that you'll need to do carry on only. And don't try to check your bags on your original flights to RGN. when you no show in HKG your bags will be offloaded and likely stuck there.

Not clear to me if you are going to cancel/modify your reservation
If you no show for any flight all subsequent flights will be cancelled.

Loosing the remaining reservation after HKG should be no problem if I understand your situation correctly.
If you have checked luggage your best bet most likely is trying to check the luggage only to HKG (with a good reason, like meeting somebody there whom you need to give something from your luggage - if you have enough time in HKG for that). Then recheck there to your new flight.
So far I have been successful in short checking luggage with a good reason.

Thanks all, I will give short checking a try if the direct redemption is still available on the day - but I don't hold much hope of being successful.

AA didn't play ball :-(

And my word, is their in flight service awful.

If you were a true bogan then you wouldn't mind - as long as they kept serving you grog of course