Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Surface Caustics
VPCAUSTICS_ENABLEDIFFUSE
Parameter: Volume Caustics
VPCAUSTICS_ENABLEVOLUME
Parameter: Strength
VPCAUSTICS_STRENGTH
Parameter: Step Size
VPCAUSTICS_STEPSIZE
Parameter: Sample Radius
VPCAUSTICS_SAMPLERADIUS
Parameter: Samples
VPCAUSTICS_SAMPLES
Parameter: Recompute
VPCAUSTICS_RECOMPUTE
Parameter: Save Solution
VPCAUSTICS_SAVESOLUTION
Parameter: Single Animation Solution
VPCAUSTICS_CAMERASOLUTION