In some games, units can add or remove borders, connections, or coatings, or may even be able to change the overall type of terrain in a cell. The actions are add-terrain, remove-terrain, and alter-terrain, respectively.
The change happens immediately (for the sake of simplicity), but in practice, you may find that preparing for the change may take awhile. For instance, the unit executing the change might have to accumulate acp or materials required for the change.