You can easily reschedule a route for a specific day. To do so, click on Route Schedule on the top ribbon bar, and then click the button that says Reschedule:
Select the existing route date, and then select the new route date. You can leave the route blank to include all routes, or select a specific route only.
Notice that the column called Assigned Date has now changed to the 23rd. To change it back to permanent date, you can simply change the date directly in the Assigned Date cell, or you if you have multiple stops to change back, you can click the Rest Assigned button towards the bottom of the Route Schedule. Make sure you do this before the Posting Your Route.