Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Index
GV_MG_DATA_INDEX
Parameter: Count
GV_MG_DATA_OCOUNT
Parameter: Local Matrix
GV_MG_DATA_OMATRIX
Parameter: Global Matrix
GV_MG_DATA_OGMATRIX
Parameter: Position
GV_MG_DATA_OGPOS
Parameter: Scale
GV_MG_DATA_OGSCA
Parameter: Rotation
GV_MG_DATA_OGROT
Parameter: Color
GV_MG_DATA_OCOLOR
Parameter: UV
GV_MG_DATA_OUV
Parameter: Visibility
GV_MG_DATA_OVISIBLE
Parameter: Weight
GV_MG_DATA_OWEIGHT