I think that section was speaking more to the fact that they have a programmatic way to create rules. I was under the impression that the "fluent" part referred the their use of the builder pattern that allowed you to string methods together in the same way a rule would appear.
But yes, you are able to change/edit/delete rules dynamically for a particular KnowledgeBase. An example can be found in their sample integration tests, or consult the KnowledgeBase docs - particularly the addKnowledgePackages(Collection<KnowledgePackage> kpackages)
and removeRule(String packageName, String ruleName)
functions.
I suppose you can combine the DescrFactory with the rule addition/creation. I'm not really able to find a public API anywhere that will help you with how to use it, and it's in the drools-compiler dependency, so I'm not certain that there will be one published as much of that artifact is meant for drools internal use.
There is also another related S/O discussion about this here.