WordPress How To: Change the Admin Greeting

admin-header.php

<?php
# wp-admin/admin-header.php
$links = array();

// Generate user profile and info links.
$links[5] = sprintf( __('Howdy, %1$s'), $user_identity );
/** ... more $links definitions ... **/
$links = apply_filters( 'admin_user_info_links', $links, $current_user );

functions.php

<?php
function rename_howdy_to_hello( $links, $current_user ) {
  $links[ 5 ] = sprintf( __( 'Hello, %1$s' ), $current_user->user_nicename );
  return $links;
}
add_filter( 'admin_user_info_links', 'rename_howdy_to_hello', 10, 2 );

special.php

<?php
function rename_howdy_to_funny_greetings( $links, $current_user ) {
	$current_hour = date('G');
	
	// default greeting
	$greeting = sprintf( __( 'Hello, %1$s' );
	
	// special greetings
	if ( $current_hour >= 22 || $current_hour < 4 ) {
		$greeting = sprintf( __( 'Hey, %1$s. Still working?' );
	}
	if ( $current_hour >= 4 && $current_hour < 10 ) {
		$greeting = sprintf( __( 'Good morning, %1$s!' );
	}
	
  $links[ 5 ] = $greeting, $current_user->user_nicename );
  return $links;
}
add_filter( 'admin_user_info_links', 'rename_howdy_to_funny_greetings', 10, 2 );

Terminal

ericteubert: ~/Sites/wordpress-single 
➜ ack Howdy
wp-admin/admin-header.php
154:$links[5] = sprintf( __('Howdy, %1$s'), $user_identity );

wp-admin/network.php
111:	'<p>' . __('Once you add this code and refresh your browser, multisite should be enabled. This screen will keep an archive of the added code. You can toggle between Network Admin and Site Admin by clicking on the Howdy (Username) dropdown in the upper right of the administration area.') . '</p>' .