you can erode any of the tiles you want.Just have to set your brush to erode change the size of it and erode away. wont be able to go over seams, but everything inside is changeable.You can even change resolutions the change them back to get say deeper eroded parts. also you could just make the terrain the size you want by using the attributes button.Change the default size toanything you want (within reason) also goto top view with the default size terrain and 16 clicks of any one arrow will move the terrain exactly flush.If you duplicate a terrain all you realy need to do is flip it x or z after it was moved by the clicks.

"Reinstall Windows" is NOT a troubleshooting step.