In Symfony, it is possible to override any bundle template by using Twig namespaces. Basically, you register an additional path for a namespace equal to the namespace of the bundle you wish to override.

However, it looks like that Sylius\Bundle\ThemeBundle\Templating\TemplateNameParser breaks this functionality as it assumes that for example @SyliusShop Twig namespace always corresponds to SyliusShopBundle bundle. In reality, @SyliusShop namespace can match any file system path as defined by twig.paths config.