Self-editing terrain?

As I was working on the HRRR I decided to run the locomotive up the line a ways to see if I had some track oddities resolved. Imagine my shock to come around the bend at the 1 1/2 mile mark and find a cliff in the track!
It appears that a single terrain tile decide it need to be 100 feet higher than it's cousins. Does anyone know why it does that? I had my first mapping project ruined when a large chunk of the hand created terrain just went to 0 altitude.
Secondly, is it possible to replace a single tile in the terrain folder? I have a situation that would be easily resolved if it can be, otherwise I'm in for a bit of work.
TIA, MM
It appears that a single terrain tile decide it need to be 100 feet higher than it's cousins. Does anyone know why it does that? I had my first mapping project ruined when a large chunk of the hand created terrain just went to 0 altitude.
Secondly, is it possible to replace a single tile in the terrain folder? I have a situation that would be easily resolved if it can be, otherwise I'm in for a bit of work.
TIA, MM