FBXImportMergeBackNullPivots -v [true|false];
FBXImportMergeBackNullPivots -q;
Assigns the rotation transformation of the null (or joints) elements in the hierarchy that are used as pre-rotation and post- rotation to the joint orient and the rotate axis of the original node.
The pre-rotation and post-rotation nodes are then deleted.
The look-up is done by name as the pre-rotation node's name contains the “__Pre_ “suffix, while the post-rotation node's name has a “__Post_” suffix.