Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Index
GV_MG_DATA_INDEXParameter: Count
GV_MG_DATA_OCOUNTParameter: Local Matrix
GV_MG_DATA_OMATRIXParameter: Global Matrix
GV_MG_DATA_OGMATRIXParameter: Position
GV_MG_DATA_OGPOSParameter: Scale
GV_MG_DATA_OGSCAParameter: Rotation
GV_MG_DATA_OGROTParameter: Color
GV_MG_DATA_OCOLORParameter: UV
GV_MG_DATA_OUVParameter: Visibility
GV_MG_DATA_OVISIBLEParameter: Weight
GV_MG_DATA_OWEIGHT