🚀 go-pugleaf

Is it possible to achieve something with an effect equivalent
to the following forms in a portable way with the MOP?

(defclass my-object (standard-object)
  ((file))
  (:metaclass my-class))

(defclass my-class (standard-class my-object)
  ((my-class-info))
  (:metaclass my-class))

The following excerpt from Chapter 6 seems to suggest that
what I want is impossible.

   Since metaobject classes may not be redefined, no behavior is specified for
   the result of calls to {\bf update-instance-for-redefined-class} on class
   metaobjects.  Since the class of class metaobjects may not be changed, no
   behavior is specified for the result of calls to {\bf
   update-instance-for-different-class} on class metaobjects.

----
  Richard Harris