I have a query regarding CUCM 5.x and later versions when you add a new subscriber to an existing CUCM cluster do i have to re-register my DLUs with the new number of nodes in cluster and is there any additional license that i have to purchase when i add a new subscriber to the cluster
You will not need to worry about DLU Licenses as they are homed to the Publisher :) You will need to acquire a new "node" license before adding the new Subscriber :)
The steps for adding a subsequent node (subscriber) are listed nicely in this doc;
Add a New Node to an Existing Cluster
Ensure that you have the appropriate number of licenses to support adding a new node.
Here is a clip from a CCM Ordering Guide
"A license must be ordered for each server in a Unified Communications Manager cluster irrespective of server function (e.g. MOH, TFTP, warm standby server, etc). **This would be the "node" license.
We know that the CCM Cluster "must" have the appropriate Node Licenses/with seats to operate correctly. In your case a "new" Node License will be required to add support for the additional Subscriber box.
It would look something like this;
Where xxxx is equal to the number of seats that are required.
Hope this helps!