Can i Regenerate Terrain by assign terrain Data On GUI

hello, everyone. Can i Regenerate Terrain by assign terrain Data On GUI? First, i regenerate the terrain already in the scene by changing its heights. i.e by using the function SetHeights().And the terrain's shape changed when i hit play. and then i plant some trees.when i quit the playing mode, the scene doesn't change,and there are also official document that says: modify terrain is permanent. The reason i think is terrain's data is saved in Terrain Data (New Terrain1) which we i see on the Inspector panel if we choose a terrain on the hierarchy panel. can i use this Terrain Data to create another terrain same as the one i regenerated. For example, go to Menu Terrain-Create Terrain and then, a new flat terrain leap to the eyes.select it and go to Terrain Data on the Inspector panel, just say 'New Terrain2', change it with the Terrain Data which i regenerated,just say 'New Terrain1', but the terrain in the scene doesn't change anymore! It goes beyond my expectation. are there anyone could explain it for me? or is there another way to save my Terrain? Any advice will be appreciate!