pretty sure Fabio means

function SPO.Pageframe1.Page2.Process.InteractiveChange
*
return dodefault()

when coding in an instance form or just

function InteractiveChange
*
return dodefault()

on a checkbox-class used as Process in SPO.Pageframe1.Page2

But while Eventhandling code allows you to add something like aspect-like programming
to classes belonging different base classes, such things can be handled via inheritance alone in vfp easier than in static languages.

Overwrite your specific InteractiveChange at first with a direct call into MyChange(), perhaps adding a this as Parameter,
to get you going and decide later if you need eventhandler or if 2 or 4 overrides in specific controls with 1-liners are enough.

Experiment later with eventhandler, when there is no deadline, but first get the fuctionality running via inheritance ;-)

my 0.02€

thomas