Board Thread:Boruto Discussions/@comment-35319087-20180415224730/@comment-33953813-20180417085826

The thing is that the seal on boruto is not exclusive to him, the leader of the Kara organization also has the same seal and we can speculate that other members of the Kara might also have a seal since there are so many kinds of them. So we can conclude that once an otsutsuki member is defeated they give a seal to the victor and so I don't think that they'd give the seals just to take over the body of that individual since I don't think that the leader of Kara or any of its memebers will allow his/her body to be taken by someone else (otsutsuki)

I think the seals are just some kind of power-ups which might be controlled by the otsutsuki to some extent.