I wonder if the trick of combining POIs would work. Was told in an AU map thread by Bushwalker8 about pooling the POIs of different maps, Topo and CN or CN and CN. This is confirmed by syzygy telling of returning Chinese tourists using two maps in a Garmin bought on holiday, one in Chinese enabled the other English disabled. Because the Western unit has no Chinese keyboard, they input in EN but are then able to negotiate to POIs on the Chinese map. Maybe might work if this map is loaded but disabled, with a modern topo as the 'visible' enabled map?