Framework development is expensive not only because of the intrinsic difficulty related to the elicitation of domain knowledge but also because of the lack of methods and techniques to support its evolution and interactive development. The present thesis proposes the use of two complementary techniques to support framework evolution: refactoring and extension rules. The refactoring technique has been developed to enable software re-structuring in a way to produce more readable and reusable code. Extension rules have been proposed to change the structure of the framework variation points by allowing the addition of new design functionalities. Both techniques preserve the observable behavior of programs. This property is formally verified in this work by using CCS approach to model checking. The proposed approach has been tested by means of a tool specially developed to support the application of the defined rules.