Mass explanation post:
You can make the terrain tiles bigger and have the water work if the number is a power of two (2,4,8,16,32,64.....) But in making the terrain bigger if stretches out the textures more and more, and the terrain looks rougher. With your instance of the isles map, you could always just plop the entire map that you want player to be able to go to in a interior box. (having a end of the world like aspect). Also in your case, you could put the main island in the center, and put other isles around the entire map. Then position and scale the box so that it has the main island in the center, and the edges almost touching the repeats of the main isle, that way, you use the repeats to actually increase the area of the map.
That code to delete it requires a engine change, so unless badspot adds it, not possible.
You can't have more then one terrain block with the standard TGE. Your only options are one or zero.