Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Shape
SPOTSHADER_GAP_SHAPEParameter: Texture
SPOTSHADER_GAP_TEXTUREParameter: Gap Color
SPOTSHADER_GAP_COLORParameter: Spot Color
SPOTSHADER_CIRCLE_COLORParameter: Scale
SPOTSHADER_SCALEParameter: U
SPOTSHADER_SCALE_UParameter: V
SPOTSHADER_SCALE_VParameter: Rotate
SPOTSHADER_ROTATEParameter: Shadow
SPOTSHADER_SHADOWParameter: Diffuse
SPOTSHADER_DIFFUSEParameter: Specular
SPOTSHADER_SPECParameter: Illumination
SPOTSHADER_ILLUMParameter: Camera
SPOTSHADER_CAMERAParameter: Lights
SPOTSHADER_LIGHTSParameter: Specular
SPOTSHADER_SPECULARParameter: Illumination
SPOTSHADER_ILLUMINATIONParameter: Shadows
SPOTSHADER_SHADOWSParameter: Invert
SPOTSHADER_INVERTParameter: Use Lights
SPOTSHADER_INCEXCParameter: Lights
SPOTSHADER_INCEXC_LIGHTS