Shoudl be as simple as colonies tbh. I can not check, do not own Intrigue, to see how and if its possible, must be an event for Governments something like "OnGovernmentChosen". Would have to check the scheme files. Hmm, that I might actually be able to do since they are all stored in the base game folder.

Edit:

OnGovernmentChanged - Only one I can see. Should still work as intended, maybe.

I would imagine you use -  DoScenarioConversation as the PreformAction then set your Conversation internal name as the StringParam:

      <Trigger>
        <OnEvent>OnGovernmentChanged </OnEvent>
        <PerformAction>
          <Action>DoScenarioConversation</Action>
          <StringParam>Gauntlets_Converstation</StringParam>
        </PerformAction>
      </Trigger>

You will need to set up a conversation as per the game rules, see one of the megaevents for an example. This is assuming Government xml files allow triggers, if not your screwed tbh.

Edit: Also as I do not have direct access tot he  Intrigue xmls I can not say wether this event will fire as and when x government is chosen, or  if the example above fires anytime you switched? Not sure tbh.