Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Radius
PRIM_PLATONIC_RADParameter: Segments
PRIM_PLATONIC_SUBParameter: Type
PRIM_PLATONIC_TYPEParameter: Switch to Updated Platonic
PRIM_PLATONIC_SWITCH_TO_UPDATED