Thanks, again, for such an interesting discussion. I wanted to see various viewpoints and you have not disappointed. In real estate photography, I am commonly expected to change a sky. I also put fire in fireplaces and photographs on TV screens. The photographs are for advertising purposes and meant to make the place look its best. I DO NOT patch damaged walls, remove power lines, or anything else that will misrepresent the property. That is unethical and can even cause trouble for the agents. Recently I photographed a house that had damaged walls in the master bath - the damage was even marked with blue tape. A couple of weeks afterward, I got a call from the agent asking me to go re-photograph the bathroom. I asked if it had been repaired and he assured me it had, so I told him it was not necessary to return and fixed it in Photoshop - after I knew the repairs had been made at the property.
With regard to the hawk, it seems to me that the third shot with the sunset colors in the sky changes the photograph to the point of altering the subject while the second one is more neutral because it just fills the dead sky in a very normal way. It seems to me that, as a general rule, alterations that could have been done in a darkroom or help re-create what the photographer actually saw are OK (unless you are Jerry Uelsmann). Other changes are a bit more problematic and may well depend on the purpose of the photograph. I think that if I am asked if I changed the sky, I probably crossed the line.
Thanks, again, for the great discussion.