I know that CARMEN JONES used the original Bizet compositions for CARMEN, but with a new setting and Hammerstein II lyrics.
Are there any other pieces of musical theatre that modify an existing score to suit a new purpose? And which stories have been musicalized by two different people (like PHANTOM, the Book of Matthew, and the FIGARO trilogy)?
(I ask because there is something I want to try adapting that has been done already- but my plans for the source material are very different.)
Borodin's music was used in Kismet; Rachmaninoff's in Anya; Grieg's in Song of Norway; Offenbach's in The Happiest Girl in the World; Schubert's in Blossom Time.
The Anastasia tale was the source for two Broadway musicals: Anya and Anastasia; the play Three Men on a Horse was the source for Banjo Eyes and Let It Ride!; Alice in Wonderland inspired But Never Jam Today and Wonderland.
Additionally, some classic stories, such as Cinderella and Peter Pan, have several different musical theatre adaptations. Depending on how broad you would like to go with this, you could also look into more opera and ballet scores. For example, more stories that have separate opera/ballet and musical theatre adaptations (Faust, Aida, Madam Butterfly, Orpheus and Eurydice, War and Peace etc), scores that were adapted from opera to ballet (Carmen again, The Merry Widow), and the like.
(By the way, random: this won't be news to ballet buffs, but for those interested in one/both of this season's Russian-themed musicals, I just happened across a pre-existing 'Anastasia' ballet which uses Tchaikovsky music for the past tsarist scenes and some electronic music for scenes with the 'modern-day' Anna Anderson claiming to be the lost Anastasia. Interesting. https://www.youtube.com/watch?v=2BuWCQ868bY)