Hi Ram -
I thought this was a little more straightforward, then I reviewed the ITTOs per the PMBOK guide and re-watched the PrepCast lessons where it talks about the outputs to both Perform Integrated Change Control and Direct and Manage Project Work, and I'm now less sure.
I can tell you that my understanding, and what seems to be reinforced in the PrepCast lesson on Direct and Manage Project Work, is that the document updates would typically occur during that process based on approved change requests that come out of the Perform Integrated Change Control process. This makes sense to me in that while the executive decision is made by the CCB, the ripple impacts that need to be updated would be takeaways for the PM to work through, which would seem to put us back into Direct and Manage Project Work.
That said, Project Management Plan Updates is also an output of Perform Integrated Change Control. There's nothing immediately obvious (to me) in the PMBOK Guide and my quick review of the PrepCast lesson on Perform Integrated Change Control that draws a distinction between these two outputs. My best guess as to the reason why this is in two places (and if someone else has a more authoritative answer, PLEASE feel free to correct me here) is that some updates are more involved than others, and those what involve work will be handled in Direct and Manage Project Work while those that require only the documentation of decisions would be addressed as part of Perform Integrated Change Control. That's just a guess, though. The PrepCast lessons certainly put the emphasis on the Direct and Manage Project Work process, however, so that's what I would recommend using as your model when studying.
(For what it's worth, I don't recall any questions where that particular distinction would have impacted the answer.)
