You can do it, but it makes the terrain less detailed and breaks water (water bricks are fine though).
Look for the attribute square size under the terrainblock. It defaults to 8 (16 in bedroom and kitchen which is why water is always broken in the bedroom), making it larger increases the size of the triangles the terrain is made out of and thus also increases the map area. I'm pretty sure it doesn't work very well if you change it to something that's not a power of two, so stick with 2, 4, 8, 16, etc.
There isn't any other way to increase the repeat distance in Blockland.