ZW, if you do it in a completely vanilla game, it shouldn't take very long, and if you have half a dozen new terrains, then you would only need to load the game once to create a desert, etc. for each of them. (If you want to include custom neighborhood stuff, that should really make very little difference to the load time. Also, I don't think you need to actually create new hoods, just change the terrains of the existing ones, if necessary removing or copying the pics from the folder, just in case the game decides to override them.