Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Rail
MG_SPLINE_RAIL
Parameter: Target
MG_SPLINE_RAIL_TARGET
Parameter: Scale
MG_SPLINE_RAIL_SCALE
Parameter: Distribution
MG_SPLINE_MODE
Parameter: Count
MG_SPLINE_COUNT
Parameter: Step
MG_SPLINE_STEP
Parameter: Per Segment
MG_SPLINE_PERSEG
Parameter: Smooth Rotation
MG_SPLINE_SMOOTH
Parameter: Offset
MG_SPLINE_OFFSET
Parameter: Offset Variation
MG_SPLINE_OFFSETVAR
Parameter: Start
MG_SPLINE_START
Parameter: End
MG_SPLINE_END
Parameter: Loop
MG_SPLINE_LOOP
Parameter: Rate
MG_SPLINE_RATE
Parameter: Rate Variation
MG_SPLINE_RATEVAR
Parameter: Random Seed
MG_SPLINE_SEED
Parameter: Volume Spread
MG_SPLINE_VOLUME_SPREAD