Back in the 1970s, I saw Sonny Terry & Brownie Magee. Sonny Terry told the story about how he was asked to play his harmonica for the opening music in the Broadway show "Finian's Rainbow".

paraphrasing:
". . .They told me that I had to play it exactly the same each night and I said that I can't, cause I always play different each time. Then they told me how much they'll pay me and I said sure, I can play it exactly the same."