Customise the 'Howdy/Hi' message in the WordPress toolbar

functions.php

<?php
//* Add this to your functions.php file. Do NOT include the opening php tag

//* Customise the 'Howdy/Hi' message in the toolbar
function howdy_message($translated_text, $text, $domain) {
    $new_message = str_replace('Howdy', 'Welcome', $text);
    return $new_message;
}
add_filter('gettext', 'howdy_message', 10, 3);