sure its possible, make a sky i think 512x 512 then save it as 32bit tga. Then extract DalaranSky.mdx or antoer sky file then convert it to mdl then type the path of the new sky u made and import it in.
thx... one more thing... are there dynamic light sources on sky models? because sometimes a sky would have like a huge sun shining, i need my sky to be completely black.