I understand your objection to replacing the sky and, in many cases, I agree. I don't want to change the subject of the photograph with a spectacular but unrelated (or unnatural) sky. But in this case, I think of the sky as emphasizing the cold, windy, wet, and volatile day rather than changing the image. That sky is much the way I recall the day. For reference, here is the image with everything else edited but the original sky.