This isn't a new request, but more of a question for the devs because recently several people have stumbled over this modding-hurdle:
If there's still time for Holy Fury, could you maybe take a look at
modifiers?
Because atm, they are more or less a mess, and it's very counter-intuitive to guess which ones could be used in which scope.
For example, disease_defence is only available in a province scope, which is at first confusing because it is used in hospitals, which at first glance seem to be holdings (although they, indeed, are in some way directly part of the province). Similarly, fertility is listed in the wiki as being applicable to holdings, but it is - like only applicable to patrician family palaces afaik. In a similar way, certain things like e.g. ai modifiers (ai_rationality etc) are only available for traits, but not character modifiers, whereas others like e.g. retinuesize are only available in character modifiers, not traits - even though both mechanics are in the same character scope.
So base line, modifiers are somewhat inconsistent in where they can be applied. To allow for more creative ways of modding, it would be helpful if they could be adjusted to a certain degree. Such as that all modifiers currently available in character modifiers are also available for traits, and vice versa. Or that all some modifiers available special holdings (hospital, tradepost, family palace) are also available in regular holdings.
Additionally, it would be great to also have some more modifiers ported to scopes where they make sense, such as build_cost_modifier being available in holdings (because that's where buildings are built), although that would be a separate request and of lesser urgency.
Well, I hope you devs have some time for modding improvements in between the time needed to implement the gazillion of Holy Fury features - and if you have, maybe consider this here