Yes, you can go for diploma or certifcation course along with your BBA. Also, to know the scope of graphic designing you can go through the below points -

There is a lot that the Indian media requires and talented graphic designers are amongst the most important people. There is a wide variety of graphic designers, art workers, design consultants design management professionals, creative directors required. One can also work at a magazine as layout editors in reputed media organizations. Moreover one can also pursue career as a graphic designer in advertising agencies, marketing firms, design studios, educational institutes, exhibits and displays, publishers and manufacturers. As per industry standards, the monthly salary of a graphic designer initially could go up to Rs 15,000-20,000. With experience and a superior publishing company you might get about 40,000 a month. As you keep climbing the ladder you will see lot of opportunity coming your way other than your regular job, from which you can make lot of money.

Hope this helps!!!