I remember one forgettable drive-in film in the 70's where I cut out an entire reel to shorten the thing and make the plot more comprehensable. Such shenannigans were common on dusk to dawn shows. I've heard of some films that were turned into two reelers.
I've got a number of video tapes that I've considered either re-editing or doing a MST2K schtick with (MST3K being one on the list.)
None of these could be shown publicly of course, but when Lucas can go back and hack Star Wars years later, I figure any film is fair game. Other edits might be to restore a film to make it closer to the original intent. The sappy ending to the original "Invasion of the Body Snatchers" ruins the film. I remember, as a kid, seeing it late one night on tv, where the station's editor had cut out that ending and left the Body Snatcher's winning. I nearly soiled myself because the film was so powerful.

Changing a film that is in release is a big "NO-NO", no matter how much we feel we know how to make it "better".
Of course I NEVER tried to shorten my late nights at the drive-in by changing-over mid-reel when only a couple cars with no heads showing were still in the lot, and everyone else had gone home. 
"Wake up little Susie, wake up!"
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John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Cell: 716-781-4036 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion
I would never dream you would have! 
PS: Where's that Oscar picture gone? Did you get done by the AMPAS?
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John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Cell: 716-781-4036 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion
Regards to all,
Michael.
In keeping in the full spirit of those rules, I never mention the word referring to somebody's uncle, which was appropriated by A.M.P.A.S. (tm)(c)(r) Whata bunch of stuft shirts.
John, you are who you are with or without awards, and your professionalism in bending to their rules says a lot more good about you than it does for them.
I nominate John for a special film-tech award. A statuette of one of the wide-screen museum usherettes in a golden tan would be a nice touch if Marty Hart would go along.
It would spruce up that picture in the left hand column! (Not that you're a bad looking guy, John, but yaknowwhaddImean?)
All in favor?
As long as my wife doesn't get the wrong idea, and think I spend my time at work with Marty's usherettes
:
http://www.widescreenmuseum.com/
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John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Cell: 716-781-4036 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion