Since the location of respawn is determined by a marker, it's as simple as moving the marker.
So, you would use a trigger to determine when you want the respawn to be moved, such as after x seconds, or when the player enters or leaves a particular area. Once this condition is met, then use the setMarkerPos command to move the respawn marker to the desired location. E.g.,
"respawn_west" setMarkerPos [x,y]
Where x and y are the coordinates (there is no z coordinate for a marker).