If you lower the pH by adding CO2, you will have more CO2 in the water. If you lower it by adding a bit of strong acid, the equation that ties CO2 concentration, KH, and pH, will no longer be true. So, the charts based on that equation will also be untrue.
Similarly, if you raise the pH by decreasing the amount of CO2 in the water, you will have less CO2 in the water. If you raise it by adding sodium bicarbonate to the water, will have a higher KH, but not less CO2.