It's very simple :)).....
Suppose my Q&A site Name is ABC. Then there will be only one page in my entire site whose title will say ABC.
So here is the code:
function head_title()
{
$pagetitle=strlen($this->request) ? strip_tags(@$this->content['title']) : '';
$headtitle=(strlen($pagetitle) ? ($pagetitle.' - ') : '').$this->content['site_title'];
if (($headtitle == "ABC"))
{
$this->output('<TITLE>NEW ABC TITLE</TITLE>');
}
else
{
$this->output('<TITLE>'.$headtitle.'</TITLE>');
}
}