I think we can safely move the conversation out of Real World and back In Setting.
In Setting, I doubt the Inquisition will have the sort of wide ranging authority some would like. The presence of Josephine strongly hints otherwise, in fact. If the Inquisition has carte blanche, like create legal definitions or try people for things no one else considers a crime, there is no need for an ambassador to negotiate with other powers.
Now, you could, in theory, have your ambassador try to negotiate for those powers, but given the state of government in Thedas, it seems unlikely that you would get them. Monarchs tend to have to be forced to give up power, and even though the Inquisitor as a person controls the Green Hand, the Inquisition as an organization needs the support of major outside powers as much as they need the Inquisition, so extortion won't be a universally effective negotiating tactic.
Again, it could happen. The writers can do whatever they want, but I don't see it as likely. Truthfully, I doubt it will even be addressed.