Adding skylights would have to be done via meshes since we're pretty darn close to the brush limit iirc, I remember that some stuff had to be simplified already because of the darn brush limit, changing the light wouldn't be that hard, just extremely time consuming due to source having to compile the light every time you want to check it.
Sadly the editor light preview is utter garbage for that.
Additionally the skybox would have to be changed entirely, there would be a lot of overlapping skybox geo if I just added new skylights.
All in all, possible, but a lot of work. Something I sadly don't have enough time for at the moment.