A customization portal provides an interface for customizing an implementation of a voice-based information retrieval system executed by a virtual assistant. The virtual assistant has been previously trained for natural language understanding (NLU) of speech input indicating selection of some menu items. For other menu items, the customization portal allows the use of context-independent signifiers (e.g., letters or numbers) or custom signifiers (e.g., free-form text) that avoid the need for NLU with respect to selection of those menu items. This approach allows the system to provide a natural-feeling conversation for the user, while also providing the flexibility to present custom menu choices and content to a user without specialized NLU training.