Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Radius
MDATA_SPLINESMOOTH_RADIUSParameter: Strength
MDATA_SPLINESMOOTH_STRENGTHParameter: Smooth
MDATA_SPLINESMOOTH_SMOOTHParameter: Flatten
MDATA_SPLINESMOOTH_FLATTENParameter: Random
MDATA_SPLINESMOOTH_RANDOMParameter: Pull
MDATA_SPLINESMOOTH_PULLParameter: Spiral
MDATA_SPLINESMOOTH_SPIRALParameter: Inflate
MDATA_SPLINESMOOTH_INFLATEParameter: Project
MDATA_SPLINESMOOTH_PROJECT