Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Camera
MGCAMERASHADER_LINKParameter: Horizontal Scale
MGCAMERASHADER_HSCALEParameter: Vertical Scale
MGCAMERASHADER_VSCALEParameter: Include Foreground
MGCAMERASHADER_CALC_FGParameter: Include Background
MGCAMERASHADER_CALC_BG