Getting accepted has to happen before the "coronation" - If not taken care of, the mechanic of ROE is dropping Prosperity, Stability and/or Regency.
Lets not make up more actions...
I was casual in the term, sorry. Basically I agree with the diplomacy point, I see it as:
Stage 1. Get the person noticed by the wider domain - some act of heroism, etc.
Stage 2. Show off their strength, piety, etc to cement their reputation in the domain.
Stage 3. Show off their leadership skills to get the wider domain seeing them as a potential leader - this probably involves giving them some sort of senior rank (master of the 7th spell, general, head of the inquisition, etc).
Stage 4. Make a major effort to get them recognised as heir.
Stage 5. They then have to actually take over...
But on a wider point on hiring, the 'click, I have a tank' approach is unhelpful, I'd rather have 3 or 4 actions with moderate DC than one with an insanely high DC, this would a) allow the cost to be 'touchable' and b) infer that the NPC is slowly being courted / introduced to the realm and so slowly winning over doubters in the domain.
The latter method might take a year or so (depending on how many similar court actions a season you can take) and would need you to track the actions (Fred the Just, promoted hireling - ally - henchman - lieutenant - heir?) but shouldn't be a problem to deal with.
Of course, you wind up with different classes of 'employee' under this method:
Hireling: Casual employee from time to time, has their own projects, may also work for other domains. Can aid actions, but is not fully accepted/trusted so does so at a penalty.
Ally: Firmly allied to domain, may have some of their own projects, but seen as one of the domain. Often called on to aid in domain actions.
Henchman: Well known in the domain as linked to the regent, some minor personal authority.
Lieutenant: Senor member of the domain in their own right. May carry out domain actions in their own right.
Heir: Seen as the heir / one of the potential heirs if the regent dies.