bulk Update post_meta with default values

You can add a new bulk action for posts with this code :

$postType = "post";


add_filter("bulk_actions-edit-" . $postType, function ($actions) {

    $actions["specialSave"] = "Special save";

    return $actions;

}, 20);


add_filter("handle_bulk_actions-edit-" . $postType, function ($sendback, $doaction, $post_ids) {

    if ("specialSave" !== $doaction) {
        return;
    }

    foreach ($post_ids as $idPost) {

        // action to do for each selected post



    }

    return $sendback;


}, 10, 3);

is a simple save is not enough to set the value, you can use this code to set the value directly for each selected post.