Not sure if it helps, but in case you receive a loop to ride from someone else ahead of time and you are able to import it into your Route Planner, you can open the loop and decide what is the closest waypoint to start that loop that is convenient to you.
Then click on that waypoint and look at the box of attributes that opens for that waypoint. One on the boxes (bottom row) has an icon of a Flag that says "Go" (to the right of teh Yellow star). If you click on that flag-icon and confirm your decision in a subsequent window that will open - the magic of MRA happens and that selected waypoint becomes your starting point and all other wypoints are automatically renumbered.
Cheers!
