> If one has a few objects of the same class +C, would it be possible to
> add a new method to just one of these objects, without all the others
> also getting that new method?
You can add a method to an object (or also a class) by adding a cons
pair (msg> . fun) to its value.
(push Obj (cons 'msg> '((X) (bar))))
(push Obj '(msg> (X) (bar)))
Internally, there is no formal difference between classes and objects.