The First Time

Music Theatre International (MTI), the group that licenses theatre organizations to perform musicals like West Side Story, strictly forbids changes of any kind to the original book, music or story. The company's website page for West Side Story specifically notes, under the "Show Billing" tab, that the cast and crew are not allowed to add the male Sharks to "America" or switch the places of the songs "Cool" or "Gee, Officer Krupke". The company notes that the license is not giving permission to perform the movie version in any way. The performance that the school in the show presents would be considered a violation of contract in real life.

Artie says at the beginning that the musical is just days away, but Rachel and Blaine are still shown to be using their scripts/sheet music. Given that Rachel was so proud of being off script while helping Kurt with his Romeo portion of the audition, it seems odd that she would still need a script after weeks of practice.