An interesting topic. I have no relevant experience as a singer/musician, but I used to be an amateur actor, and I can tell you that directors often make changes to plays. (Not counting the small changes that actors make inadvertently by misremembering their lines.)

Let's start with Shakespeare. Now you'd think Shakespeare's words, more than those of any other writer, would be considered sacrosanct, but probably no author is more often "edited" than Shakespeare. It is the exception, rather than the rule, for Shakespeare's plays to be performed "as written." While it's true that directors today seldom ADD any words to Shakespeare, they often delete parts of speeches, whole speeches, whole characters, and whole scenes.

And up to the nineteenth century, even the great actors used scripts that had been tinkered with a great deal—more so than we would tolerate today. (See this link to Colly Cibber's The Tragical History of Richard III, or this article about Nahum Tate's King Lear. This version even has a happy ending! The text is here.)

I probably don't even need to tell you about what happens to the scripts of Hollywood movies, but a writer who whined about his screenplay being altered would probably be laughed out of town.

It's too bad you had to deal with the author directly. I have a hunch if you had gone through his agent or editor, the agent or editor would have tried to talk some sense into him. On the other hand, if you had gone through the agent or editor, you might have had to pay for the privilege of recording his work.

Ian, can you post any links to web sites you mentioned?