The cockpit isn't pressurised separately. It's possible to alter oxygen masks deployment, I know for sure it must be done landing at some altitude airports like

The cockpit isn't pressurised separately. It's possible to alter oxygen masks deployment, I know for sure it must be done landing at some altitude airports like Quito which are higher up than normal cabin altitude. De pressurizing the plane would be extremely dangerous anyway, even with your oxygen mask on. Among other things the cabin temperature would drop to -50°C or so, the low pressure could induce fatal embolism, loss of consciousness, etc.