優先順位

• src/Eccube/Kernel.phpでboot処理を行う。
• サービスや、ルーティングには優先順がある。(以下のコードで後勝ちで設定が上書きされる)

    protected function configureContainer(ContainerBuilder $container, LoaderInterface $loader)
    {
        $confDir = $this->getProjectDir().'/app/config/eccube';
        $loader->load($confDir.'/services'.self::CONFIG_EXTS, 'glob');
        $loader->load($confDir.'/packages/*'.self::CONFIG_EXTS, 'glob');
        if (is_dir($confDir.'/packages/'.$this->environment)) {
            $loader->load($confDir.'/packages/'.$this->environment.'/**/*'.self::CONFIG_EXTS, 'glob');
        }
        $loader->load($confDir.'/services_'.$this->environment.self::CONFIG_EXTS, 'glob');

        // プラグインのservices.phpをロードする.
        $dir = dirname(__DIR__).'/../app/Plugin/*/Resource/config';
        $loader->load($dir.'/services'.self::CONFIG_EXTS, 'glob');
        $loader->load($dir.'/services_'.$this->environment.self::CONFIG_EXTS, 'glob');

        // カスタマイズディレクトリのservices.phpをロードする.
        $dir = dirname(__DIR__).'/../app/Customize/Resource/config';
        $loader->load($dir.'/services'.self::CONFIG_EXTS, 'glob');
        $loader->load($dir.'/services_'.$this->environment.self::CONFIG_EXTS, 'glob');
    }

    protected function configureRoutes(RouteCollectionBuilder $routes)
    {
        $container = $this->getContainer();

        $scheme = ['https', 'http'];
        $forceSSL = $container->getParameter('eccube_force_ssl');
        if ($forceSSL) {
            $scheme = 'https';
        }
        $routes->setSchemes($scheme);

        $confDir = $this->getProjectDir().'/app/config/eccube';
        if (is_dir($confDir.'/routes/')) {
            $builder = $routes->import($confDir.'/routes/*'.self::CONFIG_EXTS, '/', 'glob');
            $builder->setSchemes($scheme);
        }
        if (is_dir($confDir.'/routes/'.$this->environment)) {
            $builder = $routes->import($confDir.'/routes/'.$this->environment.'/**/*'.self::CONFIG_EXTS, '/', 'glob');
            $builder->setSchemes($scheme);
        }
        $builder = $routes->import($confDir.'/routes'.self::CONFIG_EXTS, '/', 'glob');
        $builder->setSchemes($scheme);
        $builder = $routes->import($confDir.'/routes_'.$this->environment.self::CONFIG_EXTS, '/', 'glob');
        $builder->setSchemes($scheme);

        // 有効なプラグインのルーティングをインポートする.
        $plugins = $container->getParameter('eccube.plugins.enabled');
        $pluginDir = $this->getProjectDir().'/app/Plugin';
        foreach ($plugins as $plugin) {
            $dir = $pluginDir.'/'.$plugin.'/Controller';
            if (file_exists($dir)) {
                $builder = $routes->import($dir, '/', 'annotation');
                $builder->setSchemes($scheme);
            }
            if (file_exists($pluginDir.'/'.$plugin.'/Resource/config')) {
                $builder = $routes->import($pluginDir.'/'.$plugin.'/Resource/config/routes'.self::CONFIG_EXTS, '/', 'glob');
                $builder->setSchemes($scheme);
            }
        }
    }

テンプレートの優先順位

1. ECCUBEROOT/app/template/[template_code]
2. ECCUBEROOT/src/Eccube/Resource/template/[template_code]
3. ECCUBEROOT/app/Plugin

テンプレートカスタマイズ

https://doc4.ec-cube.net/design_template

Twigを完全に上書きするのではなくJSで介入する方法