Harry:
Yes, changing stock dimensions on a double rifle can change regulation. Does this rifle have a pad on it now? If so, how thick? If it does, remove it and check regulation with that. I don't think removing an inch would be a problem, but each gun is a law unto itself. I added a half inch to one of mine with no problems, but have never shortened one.
I hear that Kodiaks are not good candidates for re-regulation because the ribs aren't soft soldered, but don't know if that's true. I suggest that you call J. J. Perodeau (580-237-7388) and run your question by him. J. J. used to build double rifles for Marcel Thys in Belgium and is a wizard at double rifle regulation issues.
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"Serious rifles have two barrels, everything else just burns gunpowder."