>>I don't think you can do that. What you are designing will need to be reinstatiated. You can't do this on the fly like you want. The class browser is the best and easiest place to do this.
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> Yes, for the classlib. But what about form? Say, I created form based on VFP base form class, but lately I decided to switch to myForm class in myLib. Right now my only actions here could be open .SCX file as a table and modified this file direcly. It's very inconvenient... But I don't want to insist, because there could be hidden problems...

The problems are what Craig is trying to explain. When a form is open in the designer, it is already "created" from its class library. You can't change a child's parents after it is born- even though the form is in design mode, in a sense, it is still alive. The only way to change an object's class is before it's born.