Don't ya hate that!

Had a similar situation recently. I was waitlisted in D for QF107 SYD-LAX which was showing skybed config. When my waitlist cleared by joy was short lived when I realised the reason was a jump in J seats from 50 to 79, which we all know means Dreamtime config. That change was about 2 weeks out. The following day's QF107 changed from Dreamtime to Skybed config .

In the end I had to change my departure day to a few days earlier and changed to QF175 BNE-LAX non-stop, which happened to be a 3-class Dreamtime config sold as 2-class, so I scored 4A and had a first class sleeper seat ^ .

I would not hold out much chance of your flight changing back to Skybed.

If you are waitlisted for Z and call to cancel the waitlist before it has cleared, you should not have any problems. But if it has cleared, I think you will be stuck in Z .