Sorry, but your mental model is wrong.
LLMs do matrix math across "a huge bunch of weights that cannot change based on anything you say", but the matrix math and results are informed (key concept here) by what you said, including the memory of what you said earlier in the discussion (and in some setups, even across discussions).
That's what a bloody prompt does.
It's entirely logic for the parent to want the LLM's matrix math + model + internal prompt, to accepts its prompt about LegalEagle and work with that, instead of arguing and giving him shit about it.
Especially since the earlier version of the model consistently worked like he wanted, and the new one consistently doesn't. He's not asking for some new unforeseen capability unknown to LLMs.