The write access happens when you refuse to provide goods or services for coins your node disagrees with.

In that case you influence transaction activity of others to be in accordance to the protocol rules of your node. Your node technically enables you to do that. But in the end, your power to influence others comes from your economic potential, not your node. It doesn't matter if you have 1 or 1000 nodes. Theoretically, you can do this even without node, in which case you cannot completely verify the settlement of the transaction yourself, but you could still exert your influence. Or in other words, your node has zero influence if you don' t connect any economic activity to it.