I have a few friends at Thapar University, so I can tell you the branch up-gradation procedure at Thapar. 

• If you want to update your branch, CGPA is not helpful. But that doesn't mean that you can't update your branch in some way.
• At the end of the first semester, there is a "December exam," which has general PCM plus topics covered in the first semester. 
• The institute forms a rank list based on the December examination result. A counseling session for all empty seats in all branches is held based on the ranking list. 
• If in the December test two students have the same marks, their JEE rank is considered to resolve the dispute. 

In general, one or two students leave each branch, so if you put in the required effort it’s not tough to upgrade your branch.