/**
 * 1. Create a custom Toggle field in your form and change the _Field Name_ and _Template Tag_ to "is_mystery_user"
 * 2. Add a "review_as_mystery_user" capability to the user role that can review as a mystery user (change this as needed)
 * 3. Add the code snippet to your website
 */

/**
 * This changes the "is_mystery_user" Toggle field in the review form to a Hidden field for specific users.
 */
function glsr_modify_is_mystery_user_field ($fields): array {
    // check if the user can review as a mystery user.
    // change as needed...
    if (!current_user_can('review_as_mystery_user')) {
        return $fields;
    }
    // This will change the "is_mystery_user" custom field type to a hidden field.
    // hidden field values cannot be tampered with!
    foreach ($fields as $field) {
        if ('is_mystery_user' === $field->original_name) {
            $field->id = '';
            $field->is_raw = true;
            $field->original_type = 'hidden';
            $field->type = 'hidden';
            break;
        }
    }
    return $fields;
}
add_filter('site-reviews-authors/update-review-form/fields/all', 'glsr_modify_is_mystery_user_field', 10, 2);
add_filter('site-reviews/review-form/fields/all', 'glsr_modify_is_mystery_user_field', 10, 2);

/**
 * This changes the HTML _value_ of the rendered {{ is_mystery_user }} template tag.
 */
function glsr_modify_is_mystery_user_template_tag_value ($value, $tag): string {
    if (empty($value)) {
        return $value;
    }
    return '👻'; // change this to your custom html string...
}
add_filter('site-reviews/custom/value/is_mystery_user', 'glsr_modify_is_mystery_user_template_tag_value', 10, 2);