Service Academies treat intended major differently than ROTC. In fact, it is quite a bit different in such that you have full control over it, at any time. You do not need permission to change. The ultimate requirement is that you have enough credits to graduate. Some career fields may require a specific major, but this is not a case where your appointment is contingent on your chosen major. ROTC scholarships on the other hand are tied to the intended major, but even then, changing between technical majors is generally permitted. It's when you switch from tech to fuzzy that things get harder (but not impossible).