So, to change the error message your visitor sees,

The following are possible reasons and solutions. Creating an Error 404 Page If your WordPress Theme does not include a template file named 404.php, you can create your own. Lost your password?" or "ERROR: The password you entered for the username xxx is incorrect. but wordpress can handle it $adminemail = get_option('admin_email'); #the administrator email address, according to wordpress $website = get_bloginfo('url'); #gets your blog's url from wordpress $websitename = get_bloginfo('name'); #sets the blog's name,

Would the same apply for the registration page? Since many readers wish to get utmost out of WordPress and create custom login page, we make this guide on how to change login error message and let you into an The WP_DEBUG feature often provides additional information. Editing an Error 404 Page Every theme that is shipped with WordPress has a 404.php file, but not all Themes have their own custom 404 error template file.

And then, you can check it from frontend. But it has no effect. Then, edit your 404 error message.