It must be possible to install a crown galley in the place reserved for the skyloft installation in the 747-8I/BBJ
However AFAIK the 747-8I/BBJ
aircraft are built according a different standard design then the airline 747-8I aircraft.
The 747-8I Airline configuration is built according Basic number block R8001 and further.
The 747-8I BBJ
configuration is built according Basic number block R8401 and further.
L/N 1434 - 747-8JK - R8401 - RC001 is the first built BBJ
L/N 1435 - 747-830 - R8001 - RC021 is the first built airline (DLH) 747-8I
IMO modification afterwards to allow for crown galley installation will be very expensive, The crown galley possibility must be factory installed (re-routed steering cables, air conditioning ducts, wire bundles and attachment points for a galley floor.) to allow for an economic crown galley installation.
Operating a twin over the ocean, you're always one engine failure from a total emergency.