The Witcher 3 expansion pass price is too tempting. But, it will not work with the boxed version of the base game. GoG has already put the below message on their site. Anyway, I have raised a support ticket asking for clarification.

The boxed PC version of the game is compatible only with the Expansion Pass sold on GOG.com

Also, no point in paying $25 (Rs 1659) for the expansion pass on GoG even if you bought the boxed pack before. You can buy the full game + expansion pass on steam for Rs. 1444 if you buy them seperately. Even more retarded is that steam sells the combo pack themselves for Rs. 1659 which is again cheaper than paying $25 + currency conversion on GoG.