Yes,

You can change your branch from one to another after moving to M.tech degree but the branch should be related means relevant to your branch, you can't just jump from Civil to Computer science.

If you were in Civil then you will get a options like Transportation Engineering, Geological Engineering, Highway and Transportation Engineering, Environmental Engineering Metro/Railway Engineering etc.

And if you were from IT then you will get options like CSE, CS&IT, CCE, SE etc.

Same for the mechanical also, you will get options like Thermal Engineering, Machine Design Propulsion Engineering, Energy Systems Engineering, etc.

Hope you find it useful.

good luck :)