With some substantive portions of the KFD, including the doctrine of God having once been a mortal man, now published in an official Church religious instruction manual, what is the doctrinal status of this concept and the KFD itself?
Anything established as doctrine in an officially published work is doctrine. that God was once a mortal man is also established elsewhere (such as Gospel Principles) without the use of the KFD.
I voted Official Doctrine. It is the backbone of the Plan of Salvation. The Plan of Salvation is what every missionary teaches perspective members. Would the Church have missionaries teaching merely theological speculation? I don't think so.