How to change OG "subscribe to group" link text? I want to customize the link text, don't want to use string overrides module for this small job.

In my template_preprocess_node() function I tried to change the #title element of the render array. But it doesn't change the link. Any ideas?

//change the "subscribe link for tribes
if ($variables['type'] == 'tribe'){
    if (isset($variables['elements']['group_group']['0']['#title'])){
        $variables['elements']['group_group']['0']['#title'] = 'Join this Tribe';
    }
}
You don't necessarily need to use the string overrides module. You can add string overrides directly in your settings.php.
$conf['locale_custom_strings_en'][''] = array(
  'Subscribe to group' =&gt; 'Join this Tribe',
);

For more information, see Change default strings (text) without using full translation system.