[Kirk Y]

Here's a quick and dirty solution.

In "includes/class_dm_threadpost.php" Find:

function verify_pagetext(&$pagetext)
	{
		if ($this->registry->options['postmaxchars'] != 0 AND ($postlength = vbstrlen($pagetext)) > $this->registry->options['postmaxchars'])
		{
			$this->error('toolong', $postlength, $this->registry->options['postmaxchars']);
			return false;
		}

Replace with:

function verify_pagetext(&$pagetext)
	{
		global $vbulletin;
		if ($this->registry->options['postmaxchars'] != 0 AND ($postlength = vbstrlen($pagetext)) > $this->registry->options['postmaxchars'] AND $vbulletin->userinfo['usergroupid'] != '6')
		{
			$this->error('toolong', $postlength, $this->registry->options['postmaxchars']);
			return false;
		}

This assumes that your Administrator Group is UsergroupID 6.

This will eliminate the limit placed on Administrators, yet maintain the established AdminCP Limits for other Users.