Articles on: Sprwt Supprt
Why does the zip code's "Zip Code", "State" and "Delivery Route" become read-only when editing?
Those three values (plus Weight when FedEx is active) form the identity of the entry, so they are locked once created. To move a zip to another route, add the zip again with the new Delivery Route and delete the old entry.
Where to find it:
/admin/zipcodes