How to Rename an Existing DAG in Exchange 2010
Technically you can’t rename an existing Database Availability Group, but you can recreate it with a new name. It's possible to do this without requiring that the databases within the DAG to reseed. Here are the steps to recreate a DAG with a new
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Read the complete post at http://www.expta.com/2012/09/how-to-rename-existing-dag-in-exchange.html