Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: MATERIAL_PAGE_PROPERTIES
MATERIAL_PAGE_PROPERTIES
Parameter: Background Reflection
SHADOWCATCHER_REFLECTION_COLOR
Parameter: Catch Shadows
SHADOWCATCHER_SHADOWS
Parameter: Shadow Strength
SHADOWCATCHER_SHADOW_STRENGTH
Parameter: Shadow Color
SHADOWCATCHER_SHADOW_COLOR
Parameter: Include Lighting
SHADOWCATCHER_SHADOW_LIGHTING
Parameter: Catch Reflections
SHADOWCATCHER_REFLECTIONS
Parameter: Reflection Strength
SHADOWCATCHER_REFLECTIONS_STRENGTH
Parameter: Reflection Mask
SHADOWCATCHER_REFLECTIONS_MASK