After the coin has been alive for couple months now, I am not certain how this can be done:
1. Let's say you already have an order to sell on Bitrex for 1,000,000 H2O - how such reduction will happen to the new format proposed by gatt13?
2. Or if you have 1,000,000 H2O in your wallet...

reducing the block reward/ original coins count can be dangerous....