FBXExportHardEdges -v [true|false];

FBXExportHardEdges -q;

Duplicates all vertices in the scene's meshes for each polygon connected to them. The vertices’ normals are set accordingly, depending on whether they are connected to a hard or smooth edge.

If two vertices are located exactly at the same position, a warning is issued, as this causes unpredictable results when FBXImportHardEdges is set to True.

This command is the script version of the Split per Vertex Normals option in the FBX Exporter. See Split per-vertex Normals.