As much time I practice my photography, I also do this in my post processing. I have been recently going thru some classes with Ricord learning true compositing. I say true because I want to make it seem like it was there. Some call this not natural photography. I call it art and, yes, photography. Just about every picture is corrected one way or another that you see on the web, in magazines, and so on. The cameras do have their limitation.
I looked at this photo from my hotel room. Out came my iPhone, and I made about four shots and looked at which one was best as far as focus. The original sky was nothing to write home about, so you got it; the sky was replaced with a sky I wanted and made it feel like a sunrise. But, most importantly, for me, a picture I like.