Once a form has been created it is possible to change its ancestor class to another form in your project.
TForm1 = class(TForm)
TForm2 = class(TForm)
Now I want to inherit TForm2 from TForm1 instead of TForm.
First, in the pascal unit we make the change:
we open the form, and view it as text (ALT+F12) and REPLACE
object Form2: TForm2
INHERITED Form2: TForm2
Thanks to J.M. Stoorvogel for providing this information on Quality Central (http://qc.borland.com)