In the software industry, Model Driven Engineering (MDE) techniques have proven useful not only for developing new software applications but for re-engineering legacy systems. However the stakeholders face costly maintenance operations due to frequent new standards and upgraded releases. Therefore, solutions ensuring a better adaptability and flexibility of modelling tools are needed. We propose an improved technique of virtual extension of meta-models with Facets that enables one to modify meta-models already in use without rebuilding completely the software product. This technique has been implemented and experimented for model alignment and evolution.