I once declared myself the owner of a human keep, killed two guards, and beat up the old lord without killing him. That was the only time ever I have successfully ordered an enemy to yield, and when he limped away I got the message of controlling the site now.
As my first lordly acts of lording, I went around the keep telling everyone there about what had happened. Surprisingly, the lords consort was the only person with positive attitude to the change of leadership. Of the remaining people, a human thought it was inevitable, and a dwarf didn't care either way.
When I got back upstairs, I found that the disposed lord had returned to the main room, apparently having decided it was his land again while I was downstairs. I told him about my takeover (in case he had forgotten) and declared my new takeover of the same site. He said it must be stopped at all cost and spat at me, so I kicked him in the groin and told him to yield again. He refused so I kicked him again, at which point the combat turned deadly and my follower/heartperson (who apparently didn't keep my claim safe while I went downstairs) attacked the lord, so we killed him and I got my keep back.
According to legends mode, my retired adventurer just wandered back into the wilderness as soon as I let her be, but it was still a funny little misadventure. Nice work Toady, I'm looking forward to the ability to keep sites, even if it's only for boasting rights.