Can I pursue higher studies (special diseases) while working after completing MBBS?

There is no dedicated study on diseases. There are predetermined sub streams like child specialist, cardiologist, heart specialist, eye specialist, skin specialist, so this means that it is divided on the basis of body parts.

To practice as a medical practitioner, you must complete your MBBS. Now, what about reversing your idea, I mean, doing other part time job along with your studies depending on your qualification?