I cloned a screen A,inherited the contents and saved the screen as B.

Is it possible in Wireframe to change the inheritance so B is not inheriting from A but from another screen C?

You can't change the inherited screen using Properties view, however you can change the screen file directly by editing the underlying XML. To edit the XML right-click on the screen file in the Project Explorer and choose Open With > Text Editor.

Let know if you need more help with this.