Even though I tend to be in the “sing what is written” camp, in my estimation, there are times when it is appropriate—or even expected—to deviate from the score when singing musical theatre. Here are some examples:
1. It is a stylistically accepted part of the genre. This is not a blanket statement for all of musical theatre, but in certain pop/rock-influenced or gospel-influenced musicals (Children of Eden, Memphis, Jesus Christ Superstar, The Color Purple) riffing or “optioning up” can be legitimate stylistic choices.
2. The piece has been around long enough that there are multiple examples of professionals singing notes that are not in the score. Some shows and songs have been done for so long by so many artists that there is a track record of ways to change the printed notes that still honor the composer’s intent but acknowledge how the piece has grown over time.
Conversely, if there is only one professional recording available and the singer does something that is not in the score, in my mind, that is not sufficient justification to sing it that way yourself. Maybe the notes were changed by the composer between the time the recording was made and the time the music was printed and published. Or maybe the composer asked the singer specifically to play around with the melody during rehearsals to see what would happen. Which leads me to…
3. If you receive permission from the composer to deviate from the score, knock yourself out! Many contemporary musical theatre composers 
are still living. When I get the chance to meet these composers, my favorite question to ask them is what degree of latitude they would like performers to take with their music. Overwhelmingly, the composers I’ve talked to prefer greater accuracy to the score.
Therefore, before changing written notes or rhythms when performing musical theatre, I would encourage singers to consider the following:
1. Do you know what the correct notes and rhythms actually are? If you have learned a song by listening to a recording, you may be surprised at how different that piece is when you sit down at a piano and plunk out the written notes. You owe it to yourself and to the composer to know what is printed in the score.
2. Have you made the effort to make the song work in your voice the way that it is written? Again, if you have learned a song from a recording, you may prefer the notes you know just because you are used to them. When you spend some time singing the notes and rhythms that are on the page, you may gain a different insight into how the composer intended the piece to be performed.
3. Does your choice to deviate from the score enhance the text and help tell the story more effectively or does it just show off something about your voice? In other words, is communicating the story in the best way possible at the heart of your intentions?
4. If you decide to make a change, is it your own interpretive choice, borne out of the text, or are you just copying what you heard someone else sing?
Once again, in much of musical theatre, there is no absolute rule as to when it is permissible to stray from the score and when we should be more strict in our presentations. Therefore, the suggestions above are guidelines to consider rather than hard-and-fast rules. But, in my opinion, in musical theatre the place where you “make it your own” is in the way you express and tell the story from within the parameters that are provided by the composer. This is where accurate musicianship is transformed into true, interpretive artistry.
