Hello Sarah,
I am not familiar with the booklet which the CAB produce, but you can certainly add anything you wish into the envelope you send. I would actually recoommend that you also return the original booklet since that has a code which contains information about your claim. If you can still do that, I would write on the original booklet that your answers in a separate booklet prepared for you by the CAB.
Hopefully someone who is familiar with this CAB booklet will be able to jump in now that I have approved your post.
Catherine
Nothing on this board constitutes legal advice - always consult a professional about specific problems 
