Well my idea is this
Change everything a total overhall, into another person thats made up.
First off put all of his pictures to private so that no one can see them.
Second Change his name, birthdate, facts, quotes, information, everything to match your made up persons
Third change his profile picture to the picture of what you want the made up persons picture to look like.
After all this is done you will need to message a bunch of people with the "new account" so they are very confused, already being friends and having conversations with someone they dont know.  They will look at the profile and check the pictures and be very confused.
You will need to make sure that the name is changed before you start doing this though i'd say that is the most important part