Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Shadow
CELSHADER_SHADOW
Parameter: Diffuse
CELSHADER_DIFFUSE
Parameter: Specular
CELSHADER_SPEC
Parameter: Illumination
CELSHADER_ILLUM
Parameter: Use Bump
CELSHADER_BUMP
Parameter: Backfacing
CELSHADER_BACKFACE
Parameter: Camera
CELSHADER_CAMERA
Parameter: Lights
CELSHADER_LIGHTS
Parameter: Specular
CELSHADER_SPECULAR
Parameter: Illumination
CELSHADER_ILLUMINATION
Parameter: Use Light Color
CELSHADER_LIGHTSCOL
Parameter: Shadows
CELSHADER_SHADOWS
Parameter: Shadows
CELSHADER_SHADOWSTYPE
Parameter: Mode
CELSHADER_SHADOWSMODE
Parameter: Invert
CELSHADER_SHADOWSMODE_INV
Parameter: Use Lights
CELSHADER_INCEXC
Parameter: Lights
CELSHADER_INCEXC_LIGHTS