Hello Amar,
It's at all not possible by the rule of AICTE in india. First year is common for all branches so you can take admission only when you will transfer your admission after first year.

Hello Amar,
If you are interested and have the will you can easily study computer science after doing mechanical engineering. Through the concepts would be totally new CSE required coding and other computer related stuff. You can easily get placements and good packages after joining CSE.