sorry shud have been clearer. Yes you both are right, only J/C class for gurantee J cabin but what I meant was using my D-ticket i still wanted to be guranteed to a Y cabin, outside of 24hour deadline. As D is a superior ticket to any of Y/B/H/K etc, I wanted to use it to force myself to economy at least, failing the J-gurantee perk.

So far no luck. Agent say "different ticket type" as an excuse, purely because cabin type for the ticket held is different to the cabin I want a gurantee in. This comes annoying seeing D is almost certainly more rich than Y-fare (which can be debatable depending on discount I got it for).