temandaki

<title><?php bloginfo('name'); ?> <?php wp_title(); ?></title>

asagidaki ile degistireceksin

<?php
   $benim_title = get_post_meta($post->ID, "title2", true);
   if ($benim_title) { ?>
                
      <title><?php echo $benim_title; ?></title>
                
   <?php } else { ?>
                
      <title><?php bloginfo('name'); ?> <?php wp_title(); ?></title>
                    
<?php } ?>

ozel alanlardan title2 olusturup karsisina titleni yazacaksin eski titleler degismeyecek.