No, increasing the acidity (lowering the pH) will not kill the weeds. Most weeds tolerate or even prefer a lower pH. The best way to control weeds will be by physically removing them or by misting the leaves with a liquid weed killer when it isn’t expected to rain for at least 24 hours. You can lower the pH by applying sulfur to the area but I wouldn’t do that. If the moss is doing well, it will create the level of acidity it prefers on its own over time.