Create a rule called “Duchies”, with the following text:

There exists a kind of claim known as a Duchy, representing major titles held in the history of the kingdom that later became defunct. As an Act of Subterfuge, an Heir may take the Forge Claim atomic action, which has the following steps:
* Add a new Claim to the Claims in the rule Claims with a name that starts with “Duchy of “.
* Set the Type to Standard (Duchy), the Strength to 0, and the disown list to blank.
* Set the Condition to “Be the Palatine of the Estate which has a name of ‘X’”, replacing X with the name of any estate you are the Palatine of and which has a Prestige of 10 or greater. (Where that Estate name is held within that condition, it is not permitted to be interpreted as anything other than an Estate name.)
* Reduce your Reputation by 12.

When a Duchy claim has an Heir added to its Disown list, if that Heir is the Palatine of the Estate named in its Condition, the Heir with the highest reputation becomes the Palatine of that Estate. (In the case of a tie, the age of those Heirs should act as a tie-breaker, with the older Heir getting the Estate. If that still results in a Tie, the Old King becomes the Palatine of that Estate.)

In the rule Claims, replace the line “a type (Minor, Irremediable, or Standard, defaulting to Standard)” with

a type (Minor, Irremediable, or Standard, defaulting to Standard), and optionally a Subtype of Duchy.

Add the following bullet point to the Appraise any Claim action in the rule Claims

* If the Claim is a Duchy and no Heirs currently hold that Claim, remove it from the subrules of Claims.