Whether you do it officially or not.... the day a flight is cancelled and bad press is received is the day the company will up the g-day callout pay and/or move to more defensive rostering.
Interestingly, the guys who I flew with who were working G-days achieved overtime by bringing flights forward into the current month... they are probably not going to fly more hours in a 2 month period; just more in the current (overtime) month. Therefore, the hours/fatigue issue is not huge.