Gadamlu, based on that theoretical method, the attacker would probably end up with a copy. In his world, he/she'd have his/her victim and etc with whatever he/she would to do him/her. In reality, the 'victim' would be as he/she was.
Glr, it is possible to affect a person's dream, but I don't know to what degree. It's possible to do so in the physical world just by whispering comments to the person. Perhaps on the astral, if the person's third eye is open enough and you had the knowledge to manage projecting into the individual's dream it might be possible to manipulate it in some other way. However, their dream is their world, not yours, so I think it is just as likely if not more likely that the would be "attacker" could become the victim. And, having not been proven so far as I am aware, this would be just a theory. It might not work like that at all.