FedEx - Change Commodities details description.

functions.php

add_filter('wf_fedex_request','wf_fedex_label_request_callback', 10, 2 );
function wf_fedex_label_request_callback($request,$order){

	$custom_product_description = 'My Product Description';
    $commodities = !empty( $request['RequestedShipment']['CustomsClearanceDetail']['Commodities'] ) ? $request['RequestedShipment']['CustomsClearanceDetail']['Commodities']: array() ;
    foreach ($commodities as $product_id => $value) {
    	$request['RequestedShipment']['CustomsClearanceDetail']['Commodities'][$product_id]['Description'] = $custom_product_description;
    }
    return $request;
}