How do I change SQL Server 2012 Availability Group DNS subdomain?
The Availability Group Listener name is a Computer Name Object (CNO) in Active Directory, not just a DNS entry:

http://technet.microsoft.com/en-us/library/ff367878(v=exchg.150).aspx

Its location in AD determines where it gets registered. If you want to create a different one somewhere else, you can create a DNS CNAME (alias) pointing to the real Availability Group Listener name:

http://technet.microsoft.com/en-us/library/ff625726(v=ws.10).aspx