I reside in India and if possible, want to pay in my own currency as I don't think my card has is yet activated for paying foreign currencies. There's no drop down selection for it on the game page.

Is there any way to change it?

IF your currency is supported (I don't know, I can only choose between $ and €) and it's only a known bug which causes it: delete your cookies.

If it's not a supported currency, you can't.
You could try using paypal if it can't be changed though.

Nope, because it's not supported. There are only several available currencies. https://www.gog.com/support/website_help/payments_pricing_promos

I see they forgot to update that list to include Brazilian reais.

But yeah, OP, rupees are not a supported currency on GOG yet. They seem to be concerned right now with expanding into Latin America, while fleshing out their support of non-Eurozone currencies and (apparently) looking at expanding into the Chinese market. INR support might be a while in coming.