Hello.
I will start from the end of your post.

Event Pull Mechanism is not related to the core of your question at all. It is just a different mechanism for delivering the *same* events. So instead of getting called (the "true" events), your code pulls them from the queue. But you will get precisely the same events either way.

To the actual question: If I understand it correctly, the answer is No; to achieve that, you would not use Subscriptions, you would use repeated Reads.

I know that some scenarios require this. For example, historians/loggers want to know that the value has stayed the same, but it has been collected again - so that it has a new timestamp. But the RequestedUpdateRate in OPC DA is really doing what you have described, setting a limit on the update rate. Unless the server effectively violates the spec by sending out more updates, and with the same value, the Reads are the only way to do it.

The newer OPC Unified Architecture has more options in this respect.

Best regards