Does reducing fresh citrus juice increase its flavor and will the flavor be damaged if it is reduced too far?
Heating citrus changes its flavor quite dramatically. When and how much to heat and reduce citrus depends on the outcome you are looking to achieve. If you want to preserve the fresh squeezed flavor, heating is not advisable. If you are looking for a more reduced, cooked down flavor, heating can be good. Certainly, the flavor will be concentrated, but it will be different from the fresh juice. Ultimately, it is the application that matters.
What are you looking to make here?
If you want something super intense, you can try adding a natural citrus oil (i.e lemon oil to lemon juice) for a more intense fragrance. If you're hoping to up the acidity you can add powdered citric acid.
Heating the juice will change the flavour quite dramatically. But you can also try dehydrating the liquid on a low temperature, or a freeze reduction.