choosing engineering major while enrolled in arts and sciences?

I was just admitted to JHU as an econ major, although I’m really interested in the applied math and statistics program as well. Since that major is offered by the engineering school and I’m technically in arts and sciences, how difficult would it be to switch majors or to double major?

In general the process of switching majors or declaring a double major at hopkins is very easy. You basically just need to fill out a form and meet with the department coordinator.
The only exception to this rule is switching into the BME department.