I had the same doubt when I got b. pharma in bits hyderabad campus and this is what I came to know when I enquired about branch change in bits hyderabad:
Branch change is just theoretically possible!!!
For vertical transfer u have to get a pointer of at least 9.5
Now this is not possible because since 2014 the syllabus pattern has been changed. So u have to study three more additional subjects thermodynamics, probability and statistics along with ur courses.
Getting such a high pointer with so many courses is extremely difficult and no one has managed to do so at least in bits hyderabad campus since 2014.
Moreover if u try to get a dual it will take 6 years.
So plz don’t join b. pharma in hope of branch change!