My son was initially not accepted and offered PSA but then received an NROTC Scholarship and has been accepted but they assigned a major to him that he may or may not be interested in. Has anyone been in this situation and been able to change their major easily? NROTC requires physics and calculus but the major he has been assigned does not. He has been told he can register for the required classes but if he cannot change majors easily what is the point?

I am probably misunderstanding so I apologize. If he stays in the major that does not require the physics, etc but wants to stay nrotc, he needs general elective classes. Can he use those 2 classes and fulfill that requirement?
If I totally misunderstand your question, ignore.

You should be able to change your major through the portal or at the NSC. Business School and Engineering would require a separate application and would be unlikely to take anyone right now, but any other majors that are not full should be available to transfer into. Like the other poster said, regardless of the major, physics and calc should count for some elective.