As per discussion in https://projects.tigase.org/boards/9/topics/6828?r=6835#message-6835 - additional option which would allow creating new nodes only by the administrators (or possibly different configuration options:

An entity may want to create a new node. Support for this feature ("create-nodes") is RECOMMENDED. However, a service MAY disallow creation of nodes based on the identity of the requesting entity, or MAY disallow node creation altogether (e.g., reserving that privilege to a service-wide administrator).