Unfortunately, you cannot use mgExportDb to convert to/from KML. This function can only be used to write older versions of OpenFlight.
The function mgRegisterImporter is used if you want to write a database importer yourself, not if you want to use an existing one.
If you want to write your own KML converter (which I doubt you do) then you would consider mgRegisterImporter.
From a product pov, this functionality is part of Creator, not the OpenFlight API. The OpenFlight API contains functionality to read/write/edit OpenFlight files, not other formats (like KML, etc).
From a technical pov, this is a Creator plugin that has Creator UI dependencies (e.g. it displays a dialog to let you control the import/exporting) so it would not be easy to make it work outside of the Creator executable. This is the case with most Creator plugins. While they contain valuable nuggets of capability, they can only function inside Creator.
