The Common App has an arts supplement option to use after you submit. But check on what is accepted for each school. What you are proposing to do is too informal. A music supplement can be very helpful for admissions if done properly.
For example:
Students who wish to submit an arts supplement will be sent, after submission of the application, a link to complete the Case Western Reserve arts supplement. You can find additional details at “http://www.case.edu/admission"” target=“_blank”>case.edu/admission.