It is currently implemented as two hidden options, one for privacy policy and one for t&c storing the timestamp of the last update/enforcement.
The user table has been extended to hold timestamps of the last acceptance date for both, these values are compared at runtime to the option values and if it is smaller the user has to re-accept.
Now if you wanted only certain users to re-accept you would either have to change the option values (doesn't work, as everybody would have to re-accept and would be semantically wrong as there has been no update) or you would have to set the values for those users to a value smaller then the option value (doesn't really work either as this somewhat causes data loss and is also semantically incorrect).
So in order to do this properly, IMHO substantial changes to the system would probably be required.