As model-driven development promotes metamodels as key assets it raises the issue of their reuse throughout a model-driven product line life cycle. One recurrent reuse need occurs when metamodeling integrated multi-language platforms: one construct from one language is integrated to constructs from other languages by generalizing it, making it more expressive. None of the metamodel assembly facilities provided by MOF and UML (import, merge and combine) or others proposed in previous work adequately addresses this need. We thus propose a new reuse and generalize facility for such purpose.