[JWait]

Upselling Links (Related Products) uses both templates and PHP. Are you saying that you cloned both and named them "required_accessories.php" and "required_accessories.tpl? Besides that you will need to change (or duplicate) the references to "related products" wherever you want the "required accessories" to appear, in product.tpl for example. Also, since they are "required" you need some method of "forcing" the customer to buy them. Are you sure you would be better off making your "required accessories" options of the product? It just seems simpler to me that way (unless there are dozens of "required" accessories).