President: I understand your question; legal yes/no. I do not know the margin of error allowed: i.e. the margins of allowance with changes. However, the debate has widened to ways that can allow changes to happen without recalculation and avoid the 'can we/can't we' conference.
One wonders if the use of i-pads has dulled peoples thinking. With tables it was common, if no critical performance consideration, to use zero headwind for assumed temp thrust calculation. It would be a bonus. There would be some captains who would reduce to a couple of degrees before the absolute limit. You now have a couple of buffers to allow changes. If the tailwind was 5kts you'd use 10kts. If there was an intersection possible you'd use that performance even if you were expecting full length, just incase ATC offers it. Being proactive, anticipating, covering last minute changes to avoid delays. Airmanship. I wonder if the use of computers has led guys to calculate to the last digit when it's not necessary without thinking?