Regarding the advantage of lighting shabbos candles with olive oil, can this be achieved with regular candles, by adding a bit of olive oil to them?
Although I haven’t seen anyone who mentions this idea, what you are writing seems to make sense. Although our candles nowadays give a nice and clear flame, however for the kabalistic benefit of having olive oil, adding some olive oil to the candles, (if they are in cups) would suffice this benefit.
As a side point, if you are going to start to light with olive oil, make sure to say that it is bli neder.
See Baal Haturim at the beginning of Parshas Titzaveh, that this idea is alluded to in the posuk .”ואתה תצוה את בני ישראל, ויקחו לכם שמן זית זך” that the word תצו”ה is the same gematria as נשי”ם צו”ה . (נשים= 400, and צו”ה are the same letters in both words). The continuation of the posuk is “ויקחו עליך שמן זית זך” meaning that when the women light their candles it should be with olive oil.