GPLv3's secretive Additional Terms

[opensource.*.nwo at neverbox.com]

Thank you John for your ingenious answers. Your section 7 answers are 
exactly the stuff I don't understand why the GNU hides from their 
otherwise good FAQ. Section 7 deserves its own section in the FAQ.

As for additional permissions, does it mean those "permission granted not 
to distribute source code"are actually legitimate? I don't see how such 
deriatives could still be GPL.

As for additional restrictions, I like to understand more a-e. Some of them 
seem like it would be a risk NOT to use them.

As for "GPLv3 plus name in the footer", I was wondering more about whether 
I can add "unless agreed otherwise" (e.g. in a written permission)?