The GRN wiki page is out of date, so I won't go ballistic on you for it. But I will explain what you need to change.
First off, we separated the noble hierarchy from military ranks. There is exactly one Grand Marshall and exactly one General. Below that, there are Colonels and Lt. Colonels and such.
The noble hierarchy is like so: The King, exactly one Duc, one Margrave per system, one Comte per planet, one Baron per station and planetside city, each reporting to the noble whose domain encompasses his own.
I am rather concerned that given that the prior system had significant similarities you wrote in a new Archduke. The title of Archduke was replaced by the title of Duc, but there was never more than one. Saying that someone other than Josef Revenant was Duc/Archduke would be a lot like saying that someone besides Louis V was king. As in "Heresy!" followed by everyone nearby trying to murder you.
There is an amount of exclusivity present in such a system. Just as you cannot call yourself "king" and expect to not be shot as a traitor, there is one Grand Marshall, one General, one Duc, and none of them are you. You will also not be taking Margrave of any system in the border worlds, or Ile-de-France, as players already exist for those.
I leave it up to you to edit your story appropriately. Be advised that claiming, in RP, to be a rank of the military or nobility that is impossible (due to there being only one of such a rank) is likely to be taken as attempting to grab power from those who the Crown decided should have it. Which is treason. Treason gets you shot.
I hope I've gotten my point across.
I'm going to throw a "page contested" flag on the page until it fits, at which point I will remove it.