Hello Sakxham, 

In the IPU CET form there is option for choosing multiple courses, if you have chosen B.Com as one of your choices there, then you are eligible to appear for the B.Com CET.  But if you have not entered that as an option and already submitted the CET form with only BCA as your choice then I'm afraid you cannot change to B. Com. The IPU correction window only allows correction in areas such as name, dob, address, etc. It won't allow you to change the CET you applied for.

Hope this helps :)