Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Spline Path
ALIGNTOSPLINETAG_LINKParameter: Rail Path
ALIGNTOSPLINETAG_RAILParameter: Tangential
ALIGNTOSPLINETAG_TANGENTIALParameter: Position
ALIGNTOSPLINETAG_POSITIONParameter: Overshoot
ALIGNTOSPLINETAG_OVERSHOOTParameter: Segment
ALIGNTOSPLINETAG_SEGMENTParameter: Axis
ALIGNTOSPLINETAG_AXIS