Replace Post-Title with variable

For hiding Title in admin panel the easiest way is using CSS. Another better way is using front-end submitting plugins.

Follwoing code help you to change post title.

add_filter( 'the_title', 'replacePostTitle', 100, 2);

function replacePostTitle($title, $id){
   if (is_feed())
       $return $title;

   //do some magic here

   return $new_title;
}