As far as I know, once a Live ID is created for a certain region, you cannot change the region.
You are able to change it for the individual services (Hotmail, etc) but the base ID remains attached to the country you registered it as. There were some problems experienced by UK residents where they had initially registered a US account for use with Zune marketplace and then changed it all to UK when they purchased a WP7 device but because it was still a US account they could not add their UK credit card for purchases in the MarketPlace.
So, it seems that you'll either need to create a new US ID but potentially have no access to your credit cards or you'll just have to wait till the WP7 launches in India.
Good luck and let me know what you try!