OK; Now is more clear to me. But I don't understand why do you need an opaque part and a transparent one in the texture.
If your intention will be to cover all of the faces, in the half-sphere with the opaque color, you don't need to include any transparency in the texture.
You only need to make 2 different mapping coordinates for each half of the sphere. You can make a simple texture which includes the textures of both sides. Or you can make two different textures, with probably would be better in this case in orther to make the variations of the top side, without altering the bottom part. In orther to use 2 textures in NWN probably, would be needed to divide the 2 halves of the sphere in two independent objects objects.