Agents can freely migrate among open MASs in order to obtain resources or services not found locally. In this scenario, agent actions should be guided for avoiding unexpected behaviour. However, open MASs are extremely dynamic and, thus, a solution for guiding agent actions is non-trivial. This work details DynaCROM, our solution for continuously supporting agents in open MASs with updated norm information. The main asset of DynaCROM is that it decreases the complexity of norm representation by using contexts. DynaCROM proposes (i) a top-down modelling of contextual norms, (ii) an ontology to explicitly represent norm semantics and (iii) a rule inference engine to customize different compositions of contextual norms. Thus, DynaCROM offers a solution for both developers to enhance their open MASs with norm information and agents to be continuously supported with precise norm information.