Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: Spline
SLA_SPLINE_OBJECT
Parameter: Background Texture
SLA_SPLINE_BACKGROUND_COLOR
Parameter: Line Texture
SLA_SPLINE_LINE_COLOR
Parameter: Fill Texture
SLA_SPLINE_FILLET_COLOR
Parameter: X Offset
SLA_SPLINE_X_OFFSET
Parameter: Y Offset
SLA_SPLINE_Y_OFFSET
Parameter: X Scale
SLA_SPLINE_X_SCALE
Parameter: Y Scale
SLA_SPLINE_Y_SCALE
Parameter: Plane
SLA_SPLINE_USE_PLANE
Parameter: Single Pixel
SLA_SPLINE_SINGLE_PIXEL_WIDTH
Parameter: Line Width
SLA_SPLINE_LINE_WIDTH
Parameter: Smooth Width
SLA_SPLINE_SMOOTH_WIDTH
Parameter: Caps
SLA_SPLINE_HAS_CAPS
Parameter: Fill
SLA_SPLINE_FILL
Parameter: Use Fill Color
SLA_SPLINE_FILL_COLOR
Parameter: Bump Width
SLA_SPLINE_BUMP_WIDTH
Parameter: Text Spline
SLA_SPLINE_TEXT
Parameter: Text
SLA_SPLINE_TEXT_TEXT
Parameter: Font
SLA_SPLINE_TEXT_FONT
Parameter: Align
SLA_SPLINE_TEXT_ALIGN
Parameter: Height
SLA_SPLINE_TEXT_HEIGHT
Parameter: H Spacing
SLA_SPLINE_TEXT_HSPACING
Parameter: V Spacing
SLA_SPLINE_TEXT_VSPACING