The design of Adaptive Hypermedia is a difficult task which can be made easier if generic systems and AH creators' models are reused. We address this design problem in the setting of the GLAM platform only made up of generic components. In this paper, we assume the GLAM platform is used to create a specific adaptive hypermedia. We present a pattern and a rule-based approach helping a AH creator in reusing its user and domain models and instances in order to make them taken into account. This semi-automatic approach takes the creator's models as specialisations of GLAM generic models and requires the creator to express a minimum set of mappings between his models and the generic ones. The process results in a merged model consisting of the generic and the corresponding specific model, being fully compliant with the GLAM adaptation model. A plug-in and experimentations in the e-learning domain have been partially designed.