Easy to say hard to do. here are the details

https://www.hmc.edu/cs/academic-policies/cross-campus-students/

Welcome to the information page for CMC, Pitzer and Scripps students who are interested in pursuing a major in CS or CS/math at Harvey Mudd College. There is extremely high demand for CS courses and CS majors and unfortunately we do not have the resources to meet all of that demand. We wish that this were not the case and strive to provide a clear timeline so that you can pursue a different program of study if necessary.

The selection of students who will be able to major in CS and CS-math depends primarily on a lottery for seats in CS 5 and CS 60. To participate in either lottery, students must submit a PERM request for the course by the end of their preregistration time.