As a parent, should I support my son's decision to change his sex?

Wow....if you both live in India and your son shared this with you, and the fact that you are even thinking about it, I feel it is already a positive sign. My answer is a very happy yes. Yes, your son has surely given a lot of thought into the matter before contemplating a sex change scenario. That is some big life change, and if your son feels that is what he needs, then why the need to stop him? It is obvious you and your opinion matter to him, which is why he shared it with you, so be by his side and support him. There will be many who will be against this, so make sure he has at least you :)