Not sure it's a good idea to sneak in new packages into 9.6 or maintenance releases in general. It creates more diversity that could lead to dpkg dependency issues when the real upgrade to the next major version comes. That's perhaps a separate discussion.
Anyhow. Since it's just a very few packages and signing is mostly scripted... And since you maintain it...
Done with python-guimessages 0.3-1 and whonix-setup-wizard 0.5-1.