Dramatica is a "first principles" theory. The research phase included a lot of story analysis, but this was to get down to the granules, and then these became the axioms from which the model was built.
From these first principles, you end up with things like the Theme Chart and Companion Pairs.
In theory, anything that doesn't violate the first principles and the method used to make the larger model would be okay. Even if it meant changing something that has been established, because the only real stick in the ground are the first principles. But, it's really unlikely that the things we think of as fundamental would change, so we treat them as unchangeable. (Especially without a clear demonstration of why they would need to be changed.) So far as I know, nobody has successfully challenged or changed anything.
That doesn't mean there aren't places to go, as you said. But I still don't understand what you mean by "add to the theory".
For instance, if you listen to the podcast on Pretty Woman, you'll hear a couple references to a "ghost character". So far, this ghost has not been "defined" inside the theory, by which I mean nobody has shown that ghost characters are examples of the Variations of the IC Domain or anything like that. But, yes, that could be added to the theory.
But if you mean something like I am guessing you mean (Armando's Instant Dramatica), that isn't adding to the theory. That's a practical tool to use the theory. And that's a different thing altogether.
PS. If you're really in doubt about who to listen to, listen to the Story Experts. We've been vetted. You'll be missing out on some other good advice, but at least you have an objective measure.