Welcome, Andy ... and enjoy your forthcoming trip.
Hmm ... I'VE never been entirely sure how far the jurisdiction of the Consular Office in *Cebu extends in such matters. However, from the replies you've received to date, the consensus of opinion suggests it's possible to exchange your CNI *there ... IF you're prepared to wait 10 days ... whereas I DO know Legal Capacity can be obtained in a straightforward single transaction by travelling to Manila [which is what my wife and I did - albeit from Mindanao].
So,... it would really seem to depend upon how much TIME you have at your disposal.