Customizing tableheader.js Sticky table Header As I am having a custom "position:fixed" top navigation bar in my admin pages, the sticky table header are being hidden behind it when I scroll-up. 

I went through tableheader.js and saw there is a Drupal.settings.tableHeaderOffset that helps change the "top" property, but I don't know where I should override it. Possible to do it in my template.php? 

Also, I would like to change the position that triggers the sticky header to change visibility from hidden to visible...

  // Track horizontal positioning relative to the viewport and set visibility.
  var hScroll = document.documentElement.scrollLeft || document.body.scrollLeft;
  var vOffset = (document.documentElement.scrollTop || document.body.scrollTop) - this.vPosition;
  this.stickyVisible = vOffset &gt; 0 &amp;&amp; vOffset &lt; this.vLength;
  this.stickyTable.css({ left: (-hScroll + this.hPosition) + 'px', visibility: this.stickyVisible ? 'visible' : 'hidden' });
You can override tableheader.js using hook_js_alter(&amp;js) {}, just replace path of file, like in example (details here).

Also you can override Drupal.settings.tableHeaderOffset value.
Thus, in template.php place something like this:

drupal_add_js('themeTableHeaderOffset() { return 200; }', 'inline');
drupal_add_js(array('tableHeaderOffset' =&gt; 'themeTableHeaderOffset'), 'setting');