Let's be honest, this isn't a hard thing. I've landed at Warnervale on several occasions in the past and there's very good chance that I'll be there again in the future.
How to deal with this circumstance.
Knowing that I need to land at Warnervale 24hrs or more from the time of landing, email them (and hope I get a response in a timely fashion)
Knowing that I have to land at Warnervale within 24hrs, call the number in ERSA with the specified request.
I'm airborne and had a last minute call to land at Warnervale. It's unavailable, go elsewhere e.g Cessnock.
I'm having an emergency and need to land, Warnervale is closest. I'm landing at Warnervale.
This doesn't seem too challenging to me, it's all circumstantial and I wouldn't pull out of aviation just for that.