Change way point while flying

Ground Control Software Mission Planner
1

Hello,
I will create one flight plan and the flight will start flying. At that time, I want to change the way point.

  1. Can I change the way point while the flight is already started flying.
  2. If it is possible, where will the flight go? the original way point or the new one?
  3. After changing the new point , can I change the way point to the original point?