i usually just do something simple like mysite741_
so the version # is always unique when i upgrade..
really up to you..
and if you THEN remove it, you really defeat the purpose of having the cookie prefix.. reason being is that anyone who hasn't come to the board, while you temporarily changed the cookie prefix won't be affected..
just change it and leave it.. and announce that everyone will need to re-login... you'll get the inevitable bitch/moaners, but that's alway the case