To prevent out-of-camera changes, good old fasioned seals might work. An official would verify your media is blank ( and of the correct regulation size for your camera resolution). Then place a contest seal on your USB (or other) port and your memory door. Upon return the seals would have to be untampered. Hmmm. Sounded OK at first but not sure folks would want the possibility of some adhesive left on their camera.
Dave
The other thing that I should point out is that since digital is elgible to win the best of show. The film shooters will consider it unfair if we get to change the white balance, crop, adjust the contrast, and sharpen.
I think that as well as the uncertainty in implementation to allow adjustments will lead them to take my first recommedation and just go with jpegs.