I figured out that you CAN in fact copy and paste terrain. This may have been figured out before, but I'v never seen anything about it.
How I Figured It Out:
I was messing around in the Terrain Palette, dragging the cursor around in boredom, making the green boxes. Then I decided to hit CTRL + C to copy it, then I pressed Ctrl + V, and what do you know--I saw a green selection box of the same size. I clicked somewhere, and I noticed the exact same terrain variation in that spot as the place I had copied! So, I tried it with hills and such, and it worked! It even works with regions, cameras, units, and doodads/destructibles. | 
