Dear Student ,

Yes .. you can do B.tech even after taking admission in B.Sc course . After confirmation of your B.tech admission(through merit /Entrance exam) , if that specific college wants Transfer Certificate or Migration Certificate , then you need to apply for Migration in your current college . generally colleges take Copy of Original Documents . Don't worry, many of the colleges don't require Migration certificate to submit but it would be good for you if can keep a copy migration with you .. specially if you have registered with your Current college's affiliated University .

hope this answer helps !