看完TYPO3CMSExtbaseUtilityExtensionUtility::configurePlugin的代码，其实比我想象的要简单:

After reading the code of TYPO3CMSExtbaseUtilityExtensionUtility::configurePlugin it is actually easier than I thought:

将以下代码添加到powermailextended的ext_localconf.php中:

Add the following code to ext_localconf.php of powermailextended:

if (!function_exists('configure_plugin_add_action')) {
    /**
     * Add a action to a existing frontend plugin
     *
     * @param string  $extensionName  The extension name (in UpperCamelCase) or the extension key (in lower_underscore)
     * @param string  $pluginName     must be a unique id for your plugin in UpperCamelCase (the string length of the extension key added to the length of the plugin name should be less than 32!)
     * @param string  $controllerName Name of the Controller
     * @param string  $newAction      Name of the action
     * @param bool $cachable       Can this action be cached?
     *
     * @see TYPO3CMSExtbaseUtilityExtensionUtility::configurePlugin
     */
    function configure_plugin_add_action($extensionName, $pluginName, $controllerName, $newAction, $cachable = true) {
        $delimiterPosition = strrpos($extensionName, '.');
        if ($delimiterPosition !== false) {
            $extensionName = substr($extensionName, $delimiterPosition + 1);
        }
        $extensionName = str_replace(' ', '', ucwords(str_replace('_', ' ', $extensionName)));

        $newAction = trim($newAction);

        $GLOBALS['TYPO3_CONF_VARS']['EXTCONF']['extbase']['extensions'][$extensionName]['plugins'][$pluginName]['controllers'][$controllerName]['actions'][] = $newAction;
        if (!$cachable) {
            $GLOBALS['TYPO3_CONF_VARS']['EXTCONF']['extbase']['extensions'][$extensionName]['plugins'][$pluginName]['controllers'][$controllerName]['nonCacheableActions'][] = $newAction;
        }
    }

}

你可以这样使用它(也可以在 ext_localconf.php 中):

You can use it like this (also in ext_localconf.php):

configure_plugin_add_action('In2code.powermail', 'Pi1', 'Form', 'debug', false);

这应该在 Typo3 7-9 中工作(因为 configurePlugin-Function 并没有真正改变).

This should work in Typo3 7-9 (as the configurePlugin-Function didn't really change).