I have attached the maintenance guide for pilots, from CASA.
Schedule 8 maintenance, sub regulation 42ZC (4)
I’m a bit hesitant to plan on changing flap during the end of a take off, there is too much going on to be doing what could have been done earlier. Also the attitude will change and a chance of a bounce if not handled correctly.
The additional drag from flap has little effect at slow speeds, so by the time it does take effect, you should be able to ascertain if there is sufficient runway or not. Nominating a go/stop location that gives sufficient length for braking may help.
I recently took off from Cameron Corner which has 700m of dirt in CJR on a warm midday. I was anxious about that and started to throttle up when still taxiing down the highway. I used two stages and significant back pressure until the nose wheel began to lift slightly, then consistently relaxed back pressure as speed increased so the wheel is only just touching or not touching the surface. Was at about 50-100′ AGL when crossed the threshold.