To render far objects ingame, you have to update the LOD (meshes of the distant objects).
But If I were you, I'd try before on a test worldspace, because it's risky on the original game.
There are several parts of the LOD, you see them if you select World LOD in the World menu of the geck :
- Terrain Meshes : a mesh just under the landscape reproduces a simplified far version of the terrain : it's very long to generate, several days (about 5 to 10 for me).
- Terrain Textures : simplified textures that are generated on the LOD terrain. It generates fast, few seconds to few minutes
- Distant Objects : Every object counted as distant, most big landscape objects and buildings. Generation is fast, but there are things to do with texture format, that are complicated.
- Trees : Same thing for trees
It's better looking in a wiki how to do exactly. It is possible to update distant objects for a worldspace, but it need to prepare a texture folder in TGA format, for the neede textures. Difficult to explain.