Code snippet to limit insured amount to 100 in the cart with Xadapter FedEx plugin https://www.xadapter.com/product/woocommerce-fedex-shipping-plugin-with-print-label/

functions.php

add_filter('wf_fedex_calculate_shipping_request', 'modify_fedex_request', 10, 2);
function modify_fedex_request($fedex_requests, $fedex_packages){
    $insurance_amount = 100;             // New Insurance amount

    foreach ($fedex_requests as $req_no => &$request) {
        if( isset($request['RequestedShipment']['TotalInsuredValue']['Amount']) ) {
            $count = 0;
            foreach( $request['RequestedShipment']['RequestedPackageLineItems'] as $key => $item ) {
                $request['RequestedShipment']['RequestedPackageLineItems'][$key]['InsuredValue']['Amount'] = $insurance_amount;
                $count++;
            }
            $request['RequestedShipment']['TotalInsuredValue']['Amount'] = $insurance_amount * $count;
        }
    }
    return $fedex_requests;
}