a second category template? Or can I ‘reset’ the $args?

Goal #1 – list all the child cats of current cat – 1 level only – (this works).

THEN, also include a link to list ALL subcats, nomatter what depth. Like this:

“Narrow search below:”
* cat A
* cat B
* cat C
View All Topics:
* all topics link

I can’t figure out where to link to – the same category.php doesn’t work because it strips most cats out (see goal #1).

I need to do the opposite of the above first Goal – I need a list of all grand-children (no direct children).

This is the code to get the list of sub-cats only (#1). Is there such a thing as a ‘reset button’ so I can call it again, except different? ??

if ( is_category() ) {
  $cat = get_query_var('cat');
  $child_cats = get_categories('child_of='.$cat);
  if ($child_cats) {
    $args = array(
      'title_li' => '',
      'echo' => 1,
'depth' => 1,
      'child_of' => $cat
    );

?>
<h2><?php single_cat_title();?></h2>
<p><?php echo category_description();?></p>
<hr>
?>
<ul>
    <?php wp_list_categories($args); ?>
<!-- can I reset this loop, and enter a link here to grand-child cats, excluding the direct child-cats? -->
</ul>

<?php } else { ?>