Заметки

Данный код срабатывает при сохранении изменений в профиле пользователя WordPress.

Синхронизирует поля из usermeta в x-profile

function xprofile_sync_bp_profile2( &$errors, $update, &$user ) {
  // Bail if profile syncing is disabled.
  if ( bp_disable_profile_sync() || ! $update || $errors->get_error_codes() ) {
    return;
  }
    // Querying data from a table "usermeta", first we get the value of the custom field "address" and substitute this value for the "Address" field of the xprofile BuddyPress
    $address = get_user_meta( $user->ID, 'address', 'true' );  
  xprofile_set_field_data( 'Address', $user->ID, $address );
  	//Similarly with other fields
    $firstname = get_user_meta( $user->ID, 'first_name', 'true' );  
  xprofile_set_field_data( 'Name', $user->ID, $firstname );
  	$lastname = get_user_meta( $user->ID, 'last_name', 'true' );  
  xprofile_set_field_data( 'Lastname', $user->ID, $lastname );
  	$description = get_user_meta( $user->ID, 'description', 'true' );  
  xprofile_set_field_data( 'Bio', $user->ID, $description );
  
  	// Querying data from a table "user"
    xprofile_set_field_data( 'E-mail', $user->ID, $user->user_email );
    xprofile_set_field_data( 'Site', $user->ID, $user->user_url );
}
add_action( 'user_profile_update_errors', 'xprofile_sync_bp_profile2', 10, 3 );

Точно так же можно осуществлять и обратную синхронизацию:

// modified Xprofile sync.
function xprofile_sync_wp_profile2( $user_id = 0 ) {

  // Bail if profile syncing is disabled
  if ( bp_disable_profile_sync() ) {
    return true;
  }

  if ( empty( $user_id ) ) {
    $user_id = bp_loggedin_user_id();
  }

  if ( empty( $user_id ) ) {
    return false;
  }
    
    // get first name
    $firstname = xprofile_get_field_data('First name',$user_id );

    // get last name
    $lastname = xprofile_get_field_data('Last name',$user_id );
    
    // get nickname
    $nickname = xprofile_get_field_data('Nickname',$user_id );
    
    // create fullname
    $fullname = trim( $firstname . ' ' . $lastname );

  bp_update_user_meta( $user_id, 'nickname',   $nickname  );
  bp_update_user_meta( $user_id, 'first_name', $firstname );
  bp_update_user_meta( $user_id, 'last_name',  $lastname  );

  global $wpdb;

        //you can modify that line to change the displayed name to something else than the nickname
  $wpdb->query( $wpdb->prepare( "UPDATE {$wpdb->users} SET display_name = %s WHERE ID = %d", $nickname, $user_id ) );
}
add_action( 'xprofile_updated_profile', 'xprofile_sync_wp_profile2' );
add_action( 'bp_core_signup_user',      'xprofile_sync_wp_profile2' );
add_action( 'bp_core_activated_user',   'xprofile_sync_wp_profile2' );

Источник второго варианта:

https://buddypress.org/support/topic/how-to-use-custom-name-fields-with-xprofile/

Добавляет произвольные поля во фронте

// Add custom fields to bbpress topics on front end
add_action ( 'bbp_theme_before_topic_form_content', 'bbp_extra_fields');
function bbp_extra_fields() {
   $value = get_post_meta( bbp_get_topic_id(), 'YOUR-FIELD-NAME', true);
   echo '<label for="bbp_extra_field">My Extra Field:</label><br>';
   echo "<input type='text' name='YOUR-FIELD-NAME' value='".$value."'>";
}

//Save and update the values from the front end
add_action ( 'bbp_new_topic', 'bbp_save_extra_fields', 10, 1 );
add_action ( 'bbp_edit_topic', 'bbp_save_extra_fields', 10, 1 );

function bbp_save_extra_fields($topic_id=0) {
  if (isset($_POST) && $_POST['YOUR-FIELD-NAME']!='')
    update_post_meta( $topic_id, 'YOUR-FIELD-NAME', $_POST['YOUR-FIELD-NAME'] );
    
}

Источник:

bbPress and custom fields