To modify custom error handling in your .htaccess file, you can use the ErrorDocument directive. This directive allows you to specify custom error pages for different HTTP status codes. Here’s a basic example:

In this example:

ErrorDocument 400 sets a custom error page for the 400 Bad Request status.
ErrorDocument 401 sets a custom error page for the 401 Unauthorized status.
ErrorDocument 403 sets a custom error page for the 403 Forbidden status.
ErrorDocument 404 sets a custom error page for the 404 Not Found status.
ErrorDocument 500 sets a custom error page for the 500 Internal Server Error status.

Make sure to replace the paths /error_pages/400.html, etc., with the actual paths to your custom error pages.

You can customize this further by creating specific error pages for other status codes or by using a generic error page for all errors:

In this case, all errors will be redirected to the same error page.

Remember to adjust the paths and filenames to match your file structure and naming conventions. After making changes to your .htaccess file, ensure that it is placed in the correct directory and that it is allowed to override server configuration by setting AllowOverride to All in your Apache configuration.