Here is exactly what I do when I try to Transfer my objects/terrain to a new Scene: (If I'm doing something wrong, please tell me.)
Copy long code of numbers from scn_my_scene_16.
Go into singleplayer terrain editor.
Make the map longer.
Paste the new code onto scn_my_scene_17 (or 18, 19, 20.)
Add the same outer terrain. (If I go into the game now I can freely edit terrain anywhere on the map.)
Copy the file inside the folder "SceneObj" named "scn_my_scene_16.sco" and then rename the copy "scn_my_scene_17.sco" (After I add this though, I cannot edit the terrain past the same point, more pictures showing the same line:
Am I doing something wrong, or is the Object file bugged or something?