If I don not get into a pharmacy school after two years of pre-pharmacy or decide not to pursue pharmacy during those two years, what options would I have? Would I be able to switch to biomedical or chemical engineering easily?
Clinical lab science is a good option
I would encourage you to drop pharmacy and pursue engineering. The job market and work environment of pharmacy is already terrible and getting worse each year as more schools graduate their first class. Engineering will provide you better job prospects, a better work environment, and better take-home pay without you having to take out $200k+ in loans and spend another 4 years in school.