Rather than changing title history, removing mayors can be accomplished through an on-action. Here's the code if you're interested:

on_game_start = {
on_actions = {
ck_remove_mayors
}
}

ck_remove_mayors = {
effect = {
every_province = {
limit = {
has_holding_type = city_holding
county_controller = { NOT = { has_government = tribal_government } }
}
county_controller = { get_title = prev.barony }
}
}
}

I had assumed something like this was possible, but way more complicated than this. This is a miracle, thank you

No problem.