(Three years later)
I found an excellent resource here which explains many of the historical and theological questions I asked.
Some excerpts are below, which answer my questions. Highlighting is my own.
Over the period of nearly 1400 years, the Islamic Salaah and the
Shahadah have not been revised. Within a period of half a century, I
have observed the Ismaili Du'a and the Ismaili Shahadah, each being
revised three times. The present Du'a in Arabic, replacing the old
Du'a in Gujrati, was formulated and officially pronounced by the
Farmans (Holy Commands) of the late Aga Khan in 1956. Since he was
suffering from lumbago, sciatica and the cancer, he sent his grandson
- the present Aga Khan, to introduce the "New Du'a" in the Eastern Africa. The "New Du'a" introduced officially in Africa had an ending:
"al-Imamul haziril maujood li zikrihis sujood." meaning:
"the present Imam, to whose name prostration is due."
When the same "New Du'a" was introduced in the Islamic State of
Pakistan,the above mentioned phrase was changed to read:
"Allahumma laka sujoodi wa ta'ati." meaning:
"O Allah, to Thee is my prostration."
Again, the same old apprehension of being labeled "apostate" by those
Pakistani Muslims, who the lack knowledge and true understanding of
the inner Ismaili gnostic, which is not so easy to comprehend.
Another interesting post here notes several things; I have abbreviated it to relevant portions:
This prayer clearly says the Aga Khan is the incarnation of Allah [...] This is part of the reason why many older Nizari Ismailis believe that Aga Khan is Allah (they were taught this) [...] Many younger Nizari Ismailis struggle to believe that Aga Khan could possibly be Allah, though. **The [...] Dua was replaced in I think 1956, with the current Dua [...] The current Dua doesn't say that Aga Khan is Allah, although it does have some elements of clear shirk.
Some people say that the Aga Khan changed the beliefs around 1950 from the Aga Khan being Allah to the Aga Khan having the Noor of Allah inside of him [...] So, now Nizari Ismailis say that Aga Khan holds the Noor of Allah inside of him, whereas before they used to say he is the same as Allah. But, many Nizari Ismailis still believe the Aga Khan is Allah even though he only says now that he has the Noor of Allah and is not the same as Allah. Pretty much anything you find on Nizari Ismailis between about 1800 and 1950 says that their Imam is the same to them as Allah. They even used to worship his picture back in those days (1800 to 1950), according to a conversation I had with an older Nizari Ismaili who confirmed that they were worshipping Aga Khan's picture back in East Africa in the jamatkhana she was at. The practice eventually stopped around 1950. It was around 1950, which was around the time Pakistan was formed and where many Nizari Ismailis were living, that the beliefs started to change [...] Around 1956 the old Dua changed into the new one (current one).
This answers both my questions of:
- Where did this book origin? It appears to be compiled by the Aga Khan in 1950-1956.
- Does this book change? Yes. It has gone through multiple revisions -- at least one around 1950, in response to theological changes. There are at least two different versions mentioned -- the original, and the one in Pakistan.
And Allah knows best.