Replace text field labels with url

// Many pieces of meta info pass through this filter, not only custom fields
add_filter('tribe_meta_factory_template', 'change_custom_fields', 20, 3);

function change_custom_fields($html, $label, $meta) {
        // We are only interested in one specific custom field
        if ('Registration' !== $label) return $html;

        // Swap out the current value for something else

        return str_replace($meta,"<a href=$meta>Click to register</a>", $html);

}