Hi aspirant, let me tell you first every IIT has it's own norms and regulations. So generally what happens suppose a student opted Mechanical Branch and now after 1-2 months he/she gained interest in other branch let say ECE, than the only thing he/she do is that he/she can change his/her branch after 1 year on behalf of their performance in their opted branch and than ask for changing his/her branch.
Thank You.
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