How can I set the "activateAccountSuccessPath" for users with Control Panel access?
You can write a plugin that listens to the users.onActivateUser event, and manually redirects the browser to your desired page.

Just add this code to your plugin’s primary class:

public function init()
{
    craft()-&gt;on('users.activateUser', array($this, 'onActivateUser'));
}

public function onActivateUser(Event $event)
{
    /* @var UserModel $user */
    $user = $event-&gt;params['user'];

    // Are they in the default group?
    // (Indicates this was probably public registration)
    if ($user-&gt;isInGroup('myDefaultGroup'))
    {
        // Redirect them to the activateAccountSuccessPath
        $activateAccountSuccessPath = craft()-&gt;config-&gt;getLocalized('activateAccountSuccessPath');
        $url = UrlHelper::getSiteUrl($activateAccountSuccessPath);
        craft()-&gt;request-&gt;redirect($url);
    }
}