Hi Romana.
As I say, I've little personal experience in this area. The Frosts have written that once projected, if you wait beside a sleeping person, at some point they will project themselves. It is then just a matter of slipping into their body and taking it for a drive (just as some might a car left idling at the side of the road).
Returning, they say, is simply the reverse, drift out and go back to your own body. They claim this is the ultimate tool for understanding someone, as you are operating their brain and body for the duration. Hence their recommendation for permanent protection ( I believe they favour a protective talisman - but don't take my word on this, it is many years since I read their book on the subject), as you are vulnerable to being under another's control if you are the possessed in this way.
I would have thought that someone taking over your body would be unlikely to linger too long, as that would leave their own shell vulnerable to your machinations also. As for driving them out - I don't recall them saying, but if I remember rightly, they discussed this whole business in their book on astral projection
www.amazon.com/Astral-Travel-Out-Body-Ex...264085409&sr=8-1