Support for dynamic and client-specific customization is required in many application areas. We present a (distributed) application as consisting of a minimal functional core – implemented as a component-based system, and an unbound set of potential extensions that can be selectively integrated within this core functionality. An extension to this core may be a new service, due to new requirements of end users. Another important category of extensions we consider, are non-functional services such as authentication, which typically introduce interaction refinements at the application level. In accordance to the separation of concerns principle, each extension is implemented as a layer of mixin-like wrappers. Each wrapper incrementally adds behavior and state to a core component instance from the outside, without modifying the component’s implementation. The novelty of this work is that the composition logic, responsible for integrating extensions into the core system, is externalize...