Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Ray Bias
SLA_DIRTY_RAY_BIAS
Parameter: Maximum Distance
SLA_DIRTY_MAX_DISTANCE
Parameter: Number of Rays
SLA_DIRTY_NUM_RAYS
Parameter: Spread
SLA_DIRTY_SPREAD
Parameter: Contrast
SLA_DIRTY_CONTRAST