Musicals and copyrights

Write your own lyrics. Collaborate with a composer when the time comes.

Music intellectual property and licensing is particularly contentious, complicated and expensive.

Even if you win, you lose because of the complications in licensing rights (often from more than one group like ASCAP and individual artists and rights holders) and the cost, which is prohibitive.

What AW Admin said -- if you have permission to use the music, you can, but be very clear on whose permissions you need and the limits of those permissions. There's often more than one person with rights to something musical, like a rap song -- composer, lyricist, potentially label, etc. Also, there's 'you can use it to write a thing,' and 'you can use it in a commercial venture,' which are two very different things and the latter can get very, very specific. You're much better off starting from scratch.

Also also, there are usually several people involved in writing a musical, as mostly book and lyrics and music are split. You can do both book and lyrics, it's not like no one has, but I'd suggest some research before you dive in.