Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Reference
GV_HIERARCHY_OBJECT_IDParameter: Reference Mode
GV_HIERARCHY_PATH_TYPEParameter: Start Position
GV_HIERARCHY_START_TYPE_IDParameter: Start Distance
GV_HIERARCHY_DISTANCE_IDParameter: Reference Path
GV_HIERARCHY_PATH_IDParameter: Start Path
GV_HIERARCHY_START_IDParameter: Iteration Path
GV_HIERARCHY_ITERATION_IDParameter: Exclude
GV_HIERARCHY_EXCLUDE_IDParameter: Maximum Iterations
GV_HIERARCHY_INPUT_MAXParameter: On
GV_HIERARCHY_OPERATOR_ONParameter: Count
GV_HIERARCHY_OUTPUT_COUNT