I think the big question is, would you re-purchase some movies if they allowed for you to be able to do it?
For instance Spider-Man 3 or Transformers 2?
Taking a piss on Picasso's grave? Disrespectful.When you go out and buy a painting for your house, do you then pick up a brush and start altering it?
Spider-Man 3 maybe but I don't think any amount of editing could save Transformers 2, at least if you still wanted a coherent film and not just action scenes back to back.