How can I modify the $submitted variable for a custom node template?
You can do this.In your theme_preprocess_node function create a new variable which is used in your node--blog_post.tpl.php .

 function yourtheme_preprocess_node(&amp;$variables) {
 $node = $variables['node'];
  if ($node-&gt;type == 'blog_post') {
    $created = $node-&gt;created;
    $date = date('F j,Y', $created);
    $name = $node-&gt;name;
    $variables['new_variable'] = "By ".$name." | ".$date;
  }
}


then print this new_variable in your tpl like this.

  &lt;div class="content clearfix"&lt;?php print $content_attributes; ?&gt;&gt;
&lt;?php
  // We hide the comments and links now so that we can render them later.
  hide($content['comments']);
  hide($content['links']);
  print render($content);
  print $new_variable;
?&gt;




Output show like this