what i mean is that you specify a list of services here, instead of classes. then in my config file i would specify additional service id instead of classes. maybe the cleanest way would be to use tagging, then you don't need defaults here, but just configuration for each of the default services to allow to disable them. to have your own tag, you need to add a compiler pass that looks for tagged services and adds calls to set them on the service that needs the strategies. a simple example is here: https://github.com/doctrine/DoctrinePHPCRBundle/blob/master/DependencyInjection/Compiler/InitializerPass.php