Ok i took the DND quite literally so to sum up: when you set your extension to DND then you have the option to route the call differently based on where the call is coming from. But you do not have the ability to answer the call on your extension. You have only the ability to forward the call. If you select forward the call to your own extension then you will create a loop, so no this will not work.
Now, there are two statuses that will allow your extension to ring. That is available and lunch. these will divert the calls accordingly but to follow the forwarding rule you will have to reach the ring timeout. And the time specified there is the same for both internal and external calls.
So the extension will ring regardless of where the call is coming through.
i think this is a request for the ideas section of the forum