c4d_base/description/flbase.hParameters are accessed with cinema::C4DAtom::GetParameter() and cinema::C4DAtom::SetParameter(). See Parameters.
Parameter: Enabled
ID_FIELDLAYER_ENABLEDParameter: Value
ID_FIELDLAYER_ENABLE_VALUEParameter: Color
ID_FIELDLAYER_ENABLE_COLORParameter: Direction
ID_FIELDLAYER_ENABLE_DIRECTIONParameter: Rotation
ID_FIELDLAYER_ENABLE_ROTATIONParameter: Layer Opacity
ID_FIELDLAYER_STRENGTHParameter: Layer Blending
ID_FIELDLAYER_BLENDINGMODEID_FIELDLAYER_BLENDINGMODE_NORMALID_FIELDLAYER_BLENDINGMODE_DARKENID_FIELDLAYER_BLENDINGMODE_TRUESUBTRACTID_FIELDLAYER_BLENDINGMODE_MULTIPLYID_FIELDLAYER_BLENDINGMODE_OVERLAYID_FIELDLAYER_BLENDINGMODE_LIGHTENID_FIELDLAYER_BLENDINGMODE_ADDID_FIELDLAYER_BLENDINGMODE_SCREENID_FIELDLAYER_BLENDINGMODE_LAYERMASK