Basically as per title.
Player can hire a new Ataman-Boyar from 4 choice-list as "Ataman", then draft him as a "Lord", but there is no apparent way to make such Ataman-Boyar to govern a province again after he is disbanded from being a "Lord".
So, either, there should be no way to draft Ataman-Boyar as a "Lord" or, preferrably, once disbanded from army such character should be in the Atamans-for-hire pool on the Atamans screen.
Also there is no way to remove an "Ataman" from his position (barring drafting him or getting him killed in a siege battle).
Also Ataman-Boyars do not get XP and have no access to inventory when being "Atamans", but when they are "Lords", they do get XP and have inventory access.