Change Named Boundary

The station value can be change from Geometry > Modify > start station, once the start station changed,  Delete the old sheet model and sheets also delete the saved view and create the new cross-section from same-named boundaries, you will able to see the changes as per newly setup station value.

I don't know of a way to change the station of a cross section named boundary, but if you only need to change one then I would just delete that particular named boundary (and associated drawing model if applicable) and recreate it at the new station location.  Be sure to add it to the existing cross section "group".  If your first sheet model references more than one cross section drawing model, then you'll need to go into the Sheet model and reference the new cross-section drawing model.  Alternatively, you can delete that sheet model and all the drawing models that are referenced to it and recreate those drawing models and sheet model from the named boundary manager.