How would you "replace" it?
If I had a more interesting sky shot, I would put it on a a layer in Photoshop below the layer with your image and, working on the layer with your image, I would mask off the sky of your image. You might have to fade in the new sky where it meets the land.
You would have to adjust the tones (sunniness) of the sky to make sure it ended up a good match with the tones (sunniness) of the land.
I am sorry I don't have your image open while I am typing this comment so I cannot be more specific. Let me know if what I suggest is unclear. I did not say it would be easy!
I think you will get more bang for your time by flipping the image as I suggested earlier. Reason is that most read/scan from left to right and, when viewers do that with your image, they end up at bright right edge and go out of the picture because there is nothing bright enough to bring them back. When the image is flipped, the bright areas will be on the left and viewers will scan across to the dark areas now on the right, which will prevent them leaving the image and they will go back to the left because it is bright and scan across with more interest.
Of course, what I suggest is speculation but it is certainly how I read pictures and I know others do likewise.
Roger