My 2 Cents
MTI, Tams-Witmark, Samuel French, Rodgers and Hamerstein, and these other licensing companies care more about their profit line then the authors integrity to the show. Why is it that HUGE REVIVALS are allowed to change things (Ex. London South Pacific, 1999 Kiss me Kate) but High Schools and a lot of Professional Theatres are not. I say this because in my experience rights to change have never been granted for a school or regional theatre production I have worked on.
I think that some shows are great as they are, and (most of the time) those are the shows that I am drawn to - If I am dying to do something and I want to make changes and not worry about copyright issues, I add a rider to my contract telling the producers that they need to obtain all rights for changes and everything like that, or they will absorb my financial liability - if they aren't up for that I will do the show Note For Note as written.
You learn to play the straight man, the lines become routine - never really saying what you mean - but i know the scene will change :)