Welcome,
Sure, I think you should be able to use the OEPocketsphinxController method changeLanguageModelToFile: in order to change between any kind of dynamically-generated files (language models, stock grammars, or RuleORama grammars). So you can create a small model or grammar for the initial interaction, testing whether a grammar or language model is more effective, and then moving to the next language model or grammar for the follow-up vocabulary phase, switching between them in realtime based on the user input.