The Spirits' Book
Book Two - The Spirit World
Chapter IX - Intervention of Spirits on the Physical World
473. Can a spirit temporarily assume the body of a living person, meaning, can it enter an animate body, and act in place of the spirit incarnated in it?
“A spirit does not enter a body the way you enter a house. It integrates itself with an incarnate spirit possessing the same flaws and qualities so that they may act in unison, but it is always the incarnate spirit who acts like he wishes upon the matter enveloping it. No other spirit can replace the one incarnated in a specific body because a spirit is inextricably tied to its body until the end of its material life.”