I know also something about the german GRPs, because I saw them in Saxony and was mapping them sometimes. I think there is no preset for that.
Actually via JOSM Editor I imported just once some lines direct to osm database, so I have not so many experience, because it is also critical if it is legal to add the data.
Normally there is something like here Category:Import from the Netherlands - OpenStreetMap Wiki
or to documentate permissions for each country.
or finding recent requests and their communication in potential datasources
For the example from Netherland, the first legal agreement to use the photo service, could be extended to a second request on the GCPs to import them.
I just asked at the forum if anyone has experience
Actually, what is BM5? BM stands for benchmarking? I often hear this, but not really understand. It is also used in osm database for tagging, like survey_point=bm_cgs in Taiwan, which also is tagged combined with satellite_point=yes. This means they connect survey point info with calibration matter.