Where did the water go that you replaced? If you pumped it out in the fall for winterization, then yes - your CYA did go down. HBow much only testing will determine.
But, if water is replaced because of evaporation then no, the CYA does not go down. When water evaporates it leaved behind the "stuff" in the water and only pure water goes away. Evaporation does not help with reductions of things like CYA, Iron, Copper or CH (calcium).