Separate Templates

i have a simple code to load separate templates for members and guests.
but i dont know where should i put this code to work! i tried init.php and engine.php, but it doesn work!

if($is_logged){
$config['skin'] = 'Default';
} 
else{
$config['skin'] = 'another';
}

i wanna make a separate templates for members and guests.

 Источник:dle-faq.pro, DLE