There is a issue in this with general terrain and site elements. Changes require a lot of work and the model gets fragmented and messy. Still looking for ideas myself. Some approaches may involve keeping elements separate for as long as possible. So the road is not joined to the terrain, but the terrain is shaped to accommodate it.
Also valiarchitects instant terrain may help. One can add items and join it together with the main terrain. then retexturing becomes an issue....