Does a MOP user really know the names of the slot where initforms and
initfunctions are stored?
 i.e.: I mean this is not portable in the sense of MOP:

      (setf (slot-value slot-definition 'clos::initform) new-initform)
      (setf (slot-value slot-definition 'clos::initfunction)

an implementation may name those slots clos::myinitform or
something...

Should one not change the slot-initform by calling
reinitialize-instance on the class with appropriate canonicalized
slot-definitions, that changes
(f :accessor f :initform "tail") to
(f :accessor f :initform "headtail")

? 


l.