It takes awhile to enact the desired change in ownership but will eventually remove the modifier on its own when it is done. No soldiers required for seizing land.

I think I understood how it exactly works:

- By setting the Seize land option, each 5 years it will take down one stack of 20% on every province of the state selected, and rise 0.25 corruption for every province affected;

- It will also deteriorate the estate's relation with you, depending which one is being affected (Burghers is 0% most of the time with me due to my constant appropriation of lands);

- By taking land to the State, you will have a bigger hold on the province administration, but will raise current governance, and give administrative debuffs if too high;

- It is possible to remove the unrest debuff after the desired percentage has reached in the provinces. It will eventually remove itself with time, but I found to be more adviseable to remove it manually.

I think this summarizes it. Knowing more of this, I enjoyed much more the administration game, and I noticed the bureaucratic setbacks in expanding ever so blindly, mainly in a Byzantium campaign.