You got it, Big D. My argument would be that if they did not change any lines, but merely the location, I don't think it adversely effects the show. if the director is re-writing the script (and we've had a few that have tried) or alter the necessary action in any way, then you have a problem.
As for adding characters, I have never really seen the need for it as they just take up space for the most part unless someone adds dialog to explain them. At the college where I used to work, it was common practice for the director to add actors/actresses to the cast in an attempt to boost the FTES (the money we receive from the state - it's based upon enrollement). Then we would have people milling around the set - when we did "Streetcar" they created all these characters (our walls were 2/4 frames with
scrim stretched over them and painted, so that you could see outside when necessary) just to walk by on occasion. It was effective, but also distracting at times.
Once we were going to tackle "Equus" and because of our college setting, the director voiced his intention of leaving out the nude scene. Lawyers wrote back and said the scene stays in or the rights will be pulled - we ended up doing "Agnes of God" instead.
If the playwright states that nothing can be changed, then it can't. however, I don't think that a set design is or should be written in concrete. The university has a director that is restaging "Forum" to Aruba - now that's stretching it farther than need be, but I've seen worse...much worse.
Char5lie