Adds an action to the order page that allows you to regenerate download permissions AND extends the expiration date for WooCommerce downloads.

wc-regenerate-and-notify.php

<?php
add_filter('woocommerce_order_actions', 'wc_regenerate_and_notify_custom_order_action');
function wc_regenerate_and_notify_custom_order_action( $actions ) {

	// Remove the woocommerce option to regenerate to avoid confusion
	unset($actions['regenerate_download_permissions']);

	// Add our new action (executed below)
	$actions['wc_regenerate_and_notify'] = __('Regenerate permissions & send link to customer', 'wc-regenerate-and-notify');
	return $actions;
}

/**
 * We need to do 4 things:
 * 1) Reset the download counter
 * 2) Reset the download expiration date
 * 3) Send order confirmation (again) with the download links
 * 4) Add a note for recording purposes. *
 */
add_action('woocommerce_order_action_wc_regenerate_and_notify', function($order){

	// 1)  Reset the download counter
	$data_store = WC_Data_Store::load( 'customer-download' );
	$data_store->delete_by_order_id( $order->ID );
	wc_downloadable_product_permissions( $order->ID, true );

	// 2) Retrieve Download and remove the access expiration. (Our poor customer has had enough trouble)
	// *Could optionally reset to product default (x days or whatever)
	$downloads = $data_store->get_downloads(array('order_id' => $order->ID) );
	if(is_array($downloads)){
		foreach($downloads as $download){
			$download->set_access_expires(null);
			$download->save();
		}
	}

	// 3 & 4) Yay! Send an updated invoice to the customer with this message:
	$order->add_order_note( __( "We've reset your download permissions. Please try downloading again.", 'woocommerce' ), true, true );
});

I really don't know anything about using code snippets and whether or not they work with wordpress actions. Your best bet is to add all of the code to your functions.php file or use the plugin version.

You would just need to change this line, using the code from my last response.

https://github.com/bdaley/woocommerce-regenerate-and-notify/blob/afaeda5f9c498f51018eaa77065951e415811b5a/woocommerce-regenerate-and-notify.php#L75