The scenario is simple: A man switches body with another. Social implications are not the issue here, but the "collateral effects" of body switching.
The Ghost Brigades is a book that touches in this matter, but is different because it's a "baby" getting into someone's mind.
How the body switching happens: it happens almost with a blink of an eye with a telephatic power of "body-spirit switching" (this is my own world lore). Only who has training in telephatic power has the ability to change bodies because the old brain will need to send/upload information through outer dimension.
How could I justify the following result?
- Long-term memories presents in the native brain will mostly remain.
- Short-term memories will be lost almost immediately.
- Movement skills will be "relearned" quickly.
- Genetic-based behavior will be preserved (or else, this would involve a body transformation, I guess. It would be a whole new discussion.)
- Certain aspects of the native personality would be preserved at the beginning, but gradually being lost as the "new mind" reshapes the brain. (At the beginning, the "new guest" will even have the impression that the native memories are his memories, but as the brain is reshaped, he will know what is his and what is not.)
- When the process is done and both brains stop the "uploading", their personalities will change because it will be as they known each other since early days. Intimancy will be very high. (just like in Pacific Rim.)
- The person will need to sleep a lot in order for the brain be reshaped. That's when the uploading begins.
(Sorry for any english grammar error, I'm not native english speaker)