what problems do you actually experience with the engine that makes you think some extra additive may solve them?
a antiwear additive may reduce wear in the valve actuation mechanism, but if you do have sufficient life already, more additive will not be of much use, although most of them double as a anti-oxidant
antifoam additives are tricky. sure, they break down foam but also they make air release properties usually a lot worse. you might thus end up without air bubbles on top of the oil and a lot of air bubbles within the oil.....not what you want to lubricate bearings with
friction modifiers only work in say the left part of the Stribeck curve, where there is mixed or boundary lubrication. thus, they will only work within the first revolutions of the engine after startup, and maybe also when shutting down. as long as you will have sufficient rpm they will have no effect, assuming that full film lubrication is present
as already mentioned by others, adding additives of unknown composition into a fully formulated oil of also unknown composition, is rather risky because, unless you have admission to suitable test equipment, the changes in performance will not be easily known.