If I had a dollar for everytime a developer asked for these capabilities.... (And I agree that they would be very useful)
But you can't with just FileMaker. The Database Design Report is the closest that you can come to this.
But there are a number of developer tool plug ins offered by third party developers. You may find that one of them offer what you want. There are some that do amazing things with an XML version Database Design Report.
I know that you can copy and paste entire scripts but that's not the thing I'm looking for here.
With FIleMaker Advanced, you can select an copy one, or a block of script steps from one script to another so you are not limited to copying entire scripts.