الجواب حامدا و مصلیا
Trading the currency of one country to earn a profit is not permissible as per Shari’ah and Haram. Therefore, taking an extra amount in exchange for new notes is also Haram due to it being interest. However, if the one possessing the new notes gives something else (even something as simple as a toffee) along with the new notes, then the one giving the old notes will be giving extra in exchange of that thing, due to which this transaction will be permissible.