How to prevent admin role from changing "Updated date" of content
You can't really, it's hard coded into the node_save() function with this bit of code:

$time = time();
if (empty($node-&gt;created)) {
  $node-&gt;created = $time;
}

// The changed timestamp is always updated for bookkeeping purposes (revisions, searching, ...)
$node-&gt;changed = $time;


Short of implementing your own node form which bypasses node_save() there's not really much you can do (except hacking the core node.module file which is never advised).