In our company either the Captain or the FO taxies the aircraft depending on who is PF. A 180 on the runway is performed best by taking a track along the centre'ish then a 30 degree cut towards the side of the runway that you are sitting on. In that case you can better judge the distance to the edge. If a tightish turn is anticipated then going over the edge is OK as long as you don't go daft - because the nose gear on the airbus is quite away back.