Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: X(t)
PRIM_FORMULA_X
Parameter: Y(t)
PRIM_FORMULA_Y
Parameter: Z(t)
PRIM_FORMULA_Z
Parameter: Tmin
PRIM_FORMULA_TMIN
Parameter: Tmax
PRIM_FORMULA_TMAX
Parameter: Samples
PRIM_FORMULA_SAMPLES
Parameter: Cubic Interpolation
PRIM_FORMULA_CUBIC