As per 2.5. Applying Custom Resource changes to running broker deployments at the moment:

You cannot dynamically update the persistenceEnabled attribute in your CR. To change this attribute, scale your cluster down to zero brokers. Delete the existing CR. Then, recreate and redeploy the CR with your changes, also specifying a deployment size.

The reason for this is that the persistence volumes are managed directly by the statefulset and autocreated by way of a template rather than "manually" created within the operator code itself.

In enabling this functionality we will want to tread carefully to ensure that if persistenceEnabled is true, and then persistenceEnabled is set to false that the user is aware that data will now be ephemeral from that point in time. Not sure of the best way to do this, but it is a concern to be addressed.