It should still work to change out un-removable civics.
I have no idea how it works for Megacorps though, that's a very interesting question.
Maybe the event can only occur for default empire types?
Edit: I looked at the game files, and it has:
Code:
trigger = {
is_country_type = default
NOT = { has_country_flag = chosen_one_ruler_event }
OR = {
has_authority = auth_democratic
has_authority = auth_oligarchic
has_authority = auth_dictatorial
}
any_owned_leader = {
OR = {
has_trait = leader_trait_admiral_chosen
has_trait = leader_trait_general_chosen
has_trait = leader_trait_governor_chosen
has_trait = leader_trait_scientist_chosen
has_trait = leader_trait_ruler_chosen
}
}
}
It looks like it can only trigger for Democratic, Oligarchic, and Dictatorial empires, none of which will be the case for Megacorps.