是的，这是可能的。如果要通过元框添加自定义字段，可以执行以下操作：

// add action to create your custom field
add_action( \'add_meta_boxes\', \'create_meta_box\'  );
// add a callback that will be called when saving the post
add_filter( \'save_post\', \'save_meta_box\', 10, 2 );

// function that will create a meta box
function create_meta_box() {
   add_meta_box(\'sample_meta_box\', __(\'Sample Box\'), \'display_meta_box\');     
}

// function that will display the actual meta box
function display_meta_box($post, $metabox) {
  ?>
   <input name="sample" type="text" id="sample" value="<?php echo get_post_meta($post->ID, \'sample\', true); ?>">
  <?php
}

// function that will be called when the post is saved
function save_meta_box($post_id, $post) {
   // default value for the field
   $value = $_POST[\'post_title\'][0];
   // only use the default value if user haven\'t specified one
   if(!empty($_POST[\'sample\'])) {
      $value = $_POST[\'sample\'];
   }
   // update the meta data for the post
   update_post_meta($post_id, \'sample\', $value);
}

如果已经通过管理界面创建了自定义字段，则可以执行以下操作：

// add a callback that will be called when saving the post
add_filter( \'save_post\', \'save_custom_field\', 10, 2 ); 

// called when updating a post
function save_custom_field($post_id, $post) {
   // loop through the meta data
   if(isset($_POST[\'meta\'])) {
     foreach($_POST[\'meta\'] as $key => $value) {
        // check if it\'s the correct field
        if($value[\'key\'] == \'sample\') {
           // this will always set the custom field to the first letter in the title
           update_post_meta($post_id, \'sample\', $_POST[\'post_title\'][0]);
           break;
        }
     }
   }
}