Hello Aspirant ,

No , You can not change your medium of reading and writing paper in the middle of class 12 as it it not allowed by any education board in India.A student have to write its class 11 and 12 in same medium so if you wrote your first term exams in Hindi you have to write your final exams in Hindi as well.

You can change it during your graduation as most of the courses In India are taught in English only.

You should not waste your time about thinking about this query go prepare for your boards exam and then if you want to study in English you can do if in your graduation.

Hope this helps.