Hi Umberto,
I'm having the same problem. I don't mind copying the .bgl to the GSX location, but some airports have multiple .bgl files (e.g. KDCA has KDCA_xxx.bgl where xxx = BLDG, GND, Handling, OBJ, PLC, PPL, Static) so I'm not sure which one to select.
Others, like EGAA only have 1x .bgl, but it's called aldergrove.bgl - will it know this is EGAA, or does the file need the ICAO in the name? Should I rename it?
Thanks for your help!