>I don't want to redefine the class library in the VCX. I want to redefine the class library of an object on a form.

Then you need to hack the scx, or the vcx - wherever the form is. Find the object's record (edit for objname="{your object's .name property}", possibly also ..."and parent=..."), then write your own in the class and classloc memos (keep in mind that classloc requires a relative path, lowercase).

Or write a builder to replace one object with another.