Mechanisms in AOP (aspect-oriented programming) can be characterized by a JPM (join point model). AOP is effective in unanticipated software evolution because crosscutting concerns can be added or removed without making invasive modifications on original programs. However, the effectiveness would be restricted if new crosscutting concerns cannot be described with existing JPMs. Mechanisms for extending JPMs are needed in order to address the problem. In this paper, an implementation framework for extending JPMs is proposed. Using the framework, we can introduce new kinds of JPMs or extend existing JPMs in the process of software evolution.