Supplemental oil additives are never advised to be added to ANY lubricant. Modern lubricants are a careful balance of components to protect from wear, control deposits and heat. Adding a little more anti wear, or more soot handling dispersant usually has undesirable effects on other aspects. e.g. more antiwear can create more piston deposits and poison exhaust catalysts.
We are constantly looking at innovative new components to add to the engine oil, and often include these in some of our fully finished formulas.