Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Surface Caustics
VPCAUSTICS_ENABLEDIFFUSEParameter: Volume Caustics
VPCAUSTICS_ENABLEVOLUMEParameter: Strength
VPCAUSTICS_STRENGTHParameter: Step Size
VPCAUSTICS_STEPSIZEParameter: Sample Radius
VPCAUSTICS_SAMPLERADIUSParameter: Samples
VPCAUSTICS_SAMPLESParameter: Recompute
VPCAUSTICS_RECOMPUTEParameter: Save Solution
VPCAUSTICS_SAVESOLUTIONParameter: Single Animation Solution
VPCAUSTICS_CAMERASOLUTION