I really don't know how they legalize or i-legalize such thing as bitcoin because you are using it with your own internet and computer hardware maybe they just not supporting it before but every citizen of India can use it no matter what happens unless their government issue a criminal liabilities in using bitcoin.
any law regarding bitcoin (legal or illegal) is always about businesses. they can never force individuals to use or not use bitcoin.
so they place laws regarding:
- trading bitcoin in exchanges (exchanges are centralized place, like a business)
- accepting bitcoin (again a physical shop or an online one is known)
if they make it illegal, the exchanges close and the shops stop accepting bitcoin.
and if they make it legal exchanges open or continue and same with shops.