Need a way/blocks to trigger a switch and held the result.

A Host vehicle (HV) is doing lane change (as shown in the image below). Once HV crossing the lane, it is necessary to swap lanes assignment at a time where lane change happens. For example, here, before lane change, left lane == lane label 3. After lane change, left lane == lane label 1. The request is that once vehicle entering the zone, change the lane assignment. (We know lane width, offset distances from lanes and HVs)