I also thought about such an edit as you proposed, but it's very difficult to remove the original background music of a movie and replace it with another one without making it sound weird, because you have to keep the dialogue and even in the center channel of a 5.1 sound there is music.
But a you should have a try. It would be great if you could accomplish something!
And there are far too few Rocky edits out there, so something has to be done^^