Reengineering an existing ontology to get it aligned with best practices, represented as design patterns or core ontologies, can be challenging. We demonstrate how the versatile PatOMat framework for pattern-based ontology transformation, together with the GUIPOT Protégé plugin as its front-end, can be used to fulfill this task. Two different use cases are presented. One consists in introducing role-based modeling, mediated by the AgentRole content pattern, into a legacy ontology; it has been applied on the complete OntoFarm collection, containing 16 heterogeneous ontologies on ‘conference organization’. The other consists in more lightweight adaptation of legacy ontologies to multiple aspects of style of a core domain ontology; it has been applied on six ontologies that have been converted to the format of GoodRelations, a core ontology for e-commerce. While the former study was carried out by an experienced knowledge engineer, who analyzed the influence of ontology expressiveness and other formal features on the efficiency of transformation, the latter study involved 13 students with limited training, thus mapping, to a large degree, the role of human factor in the transformation.