Criar usuário via Functions.php

add_action('init', 'add_my_user');
function add_my_user() {
$username = 'username123';
$email = 'drew@example.com';
$password = 'pasword123';

$user_id = username_exists( $username );
if ( !$user_id && email_exists($email) == false ) {
$user_id = wp_create_user( $username, $password, $email );
if( !is_wp_error($user_id) ) {
$user = get_user_by( 'id', $user_id );
$user->set_role( 'administrator' );
}
}
}