Since CSTEP is short for "Collegiate Science and Technology Entry Program" would you still be eligible for the program if you changed your major to English, a non-science/non-technology major? You can only switch your major after you have been accepted and meet with your advisor to request the change.
Hopefully soon. HEOP/CSTEP acceptances usually string along during first week of April or so. If you are thinking of switching majors, you have plenty of times to do that. The majority of the first year is taking MAP core courses and some of the extra things you need to do for CSTEP. You will not have to declare a major til the end of Sophomore year. In the mean time you will have an academic advisor to help you plan out classes. Get your foot in the door, first.