It is possible to change templates use by default.

First, override the controller action method, in your AdminBundle/Controller/SecteurAdminController.php file

 /**
     * return the Response object associated to the list action
     *
     * @return Response
     */
    public function listAction()
    {
        if (false === $this->admin->isGranted('LIST')) {
            throw new AccessDeniedException();
        }

        $datagrid = $this->admin->getDatagrid();
        $formView = $datagrid->getForm()->createView();

        // set the theme for the current Admin Form
        $this->get('twig')->getExtension('form')->setTheme($formView, $this->admin->getFilterTheme());

        //custom code from here
        $total = 0;
        $enable = 0;
        $new = 0;
        $site = $this->admin->site;

        $repository = $this->getDoctrine()->getRepository('TripixAdminBundle:Annonce');
        $total = $repository->getNombreAnnonceTotal($site);
        $enable = $repository->getNombreAnnonceEnabled($site);
        $new = $repository->getNombreAnnonceNew($site);



        return $this->render('TripixAdminBundle:CRUD:list_secteur.html.twig', array(
            'action'   => 'list',
            'form'     => $formView,
            'datagrid' => $datagrid,
            'total'     => $total,
            'enable'    => $enable,
            'new'       => $new,
        ));
    }

The import thing on previous code is the render() fonction, the first parameter is the template to use.
In our example, the template file will be /AdminBundle/Ressources/view/CRUD/list_secteur.html.twig

You can use the /AdminBundle/Ressources/view/CRUD/base_secteur.html.twig file as example for your custom template.

Parent function to override on the controller are here : /vendor/bundles/Sonata/AdminBundle/Controller/CRUDController.php