It doesn't appear that there were any structural modifications. As was alluded to here, apparently there were a bunch of cell phones being charged on a couple of extensions.
I think the captain might be exposed because there was no night watch walking about and it appears that this is required (even as it may not be regularly enforced).
To me, the issue is that there was no watchstanding during the night. A required watch would have addressed the fire immediately and sounded an emergency alarm. LIPO batteries being charged can emit toxic gases when overheating occurs. It’s my opinion that everyone was charging their camera batteries overnight- they ( the batteries ) got hot and started a full blown fire directly above the berthing area - impossible evacuation access plus toxic gas from the melting batteries doomed the sleeping divers