add_filter('wcfmmp_shipping_weight_calculate_amount', function( $amount, $price, $products, $destination_country, $destination_state, $weight_array_for_country, $default_cost_for_country, $total_weight, $weight_mode_for_country, $unit_cost_for_country ) {
    if( 'FR' == $destination_country && 'FR-2A' == $destination_state ) {
        $amount += 25;
    }
    return $amount;
}, 10, 10 );