Modify Howdy in Admin Bar https://wp.me/p1lTu0-hw4

functions.php

add_filter( 'admin_bar_menu', 'replace_howdy', 25 );
function replace_howdy( $wp_admin_bar ) {
    $my_account = $wp_admin_bar->get_node('my-account');
    $newtitle = str_replace( 'Howdy,', 'Welcome,', $my_account->title );
    $wp_admin_bar->add_node( array(
        'id' => 'my-account',
        'title' => $newtitle,
    ) );
}