How can PHP be used to change the URL structure while still being able to retrieve parameters using GET?

To change the URL structure while still being able to retrieve parameters using GET in PHP, you can use mod_rewrite in your .htaccess file to rewrite the URLs. This allows you to have clean and user-friendly URLs while still being able to access parameters using $_GET in your PHP code.

```php
RewriteEngine On
RewriteRule ^products/([0-9]+)$ product.php?id=$1 [L]
```

In this example, a URL like "example.com/products/123" will be rewritten internally to "example.com/product.php?id=123", allowing you to retrieve the id parameter using $_GET['id'] in your PHP code.