This have been talked about a number of time Before but it seems quite a few here want the ability to convert holdings into Another type, like maybe the front line have moved and you want to replace your Castles with cities but in CK2 that can't be done.
From what I can tell, CK2 holdings are all cities (or similar) and differentiated by who is in Power and this did sometimes change, like cities became free cities and such.
Penalty to change holding could be a large amount of gold and loss of all buidlings that are specific to the replaced holding. Maybe loss of Control to represent the problems that come with replacing the ruling class and maybe loss of some popular opinion.
From what I can tell, CK2 holdings are all cities (or similar) and differentiated by who is in Power and this did sometimes change, like cities became free cities and such.
Penalty to change holding could be a large amount of gold and loss of all buidlings that are specific to the replaced holding. Maybe loss of Control to represent the problems that come with replacing the ruling class and maybe loss of some popular opinion.