In the first instance Byakko is correct, though I think we should call them essences rather than entities, it would be less confusing since that was what Cobweb called them when she asked her question. Another essence could prevent you from regaining your rightful place in the body if it were strong enough Cobweb, though it would have to be extremely strong as the bond between you as the rightfully owning essence and the body would be very hard to break. The body would already be tuned to your vibration and it would take a lot of work to retune it to perform for someone else.
However in the second instance Byakko is mistaken. I have never heard of a multiple being created in such a violent and aggresive manner. Multiples are usually created when subsequent essences emerge in order to help the first essence with something it is not equipped to handle alone.
And this is absolutely nothing like a walk-in, where the essence has been removed or has removed itself and so has relinquished all claims on the body, at least for now. Or where the essence already in the body moves over for a new essence to take the body where it is for some reason (usually accident, trauma, or illness) unable to take it itself.
For a correct and even scientifically accepted discription of a Walk-In please read this section of the web-site which I admit with shame has been under construction since last year.
http://otherkin.30.forumer.com/index.php?showtopic=91
Thankyou.
Lady C.