How easy is it to switch between programs during your undergraduate studies?

As someone who is thinking about applying to Boston and wanting to study physics/astronomy, I was wondering how easy it is to potentially switch between the two programs. This is due to the fact that I am still not one hundred percent sure on whether or not I want to double own on studying astronomy right now or if I want to study physics generally at first.

So my question is not only on the ease of switching between the two courses, but also what kind of differences i should expect between the two courses and whether I will gain some advantages/disadvantages in these two respective programs.