Is it permissible to deal with shop owners to withdraw a sum of money from the the governmental food stamp card in exchange for them taking a percentage, knowing that this is considered usury (riba)?

It is not permissible to use deception to obtain a grant, as this violates the Hadith (definition): "Muslims are bound by their conditions." If, in addition to that, 100 is sold for 90, then this is usury (riba), as equality and immediate possession (qabd) are required when exchanging currency of the same type. If the card is designated for food, then it is forbidden to sell it before taking possession of it. One should adhere to the conditions of the grant and return what was taken unlawfully to the granting authority, or spend it on general Muslim welfare if it cannot be returned.