Apparently in the sending address book, it is possible to edit the address field of an address/label row.
Doing so, however, has 2 pretty big bugs:
Bug 1 (since 0.17, #10244): Instead of moving the label, the new address’s label was set to the new address itself, and the actual label was lost completely.
Bug 2 (effectively since 0.19, #13756): All metadata associated with the old address (prior to edit) is deleted, except for label and purpose. Probably some should remain with the old address (eg, whether the associated key was used to spend already), and others should be moved to the new address (no existing cases, just hypothetically). I doubt we should ever just outright delete it.
Edit: Bug 3 (unconfirmed, debatable): Editing both the label and address in the label-editing dialog would still delete the label for the old address.
Proposed resolution: Remove the ability to edit the address field. It doesn’t really make sense.