Hello

First of all there are no disadvantages although it is advisable that you should not change your stream in MTech but that dosent affect anything. You can always go for coding there are no restrictions and if your skills are good companies like Google,Microsoft would accept you anyway.

Also these companies dont only look for CSE Grads they look for other streams too. So go for it if you like that field, you know you can excel at it.

Hope it helps.