Migrating Exchange 2007 to Exchange 2013

Hello I have an Exchange 2007 server (CAS (HUB (MBX) on Windows 2008 with this infrastructure:

Site A
--------
- Exchange Server 2007
- Email Users

Site B
--------
- Exchange Server 2013 Backend and Frontend

Other Sites
-------------
- Email Users

Users now have access to sitema current email (Exchange 2007) by mail.contoso.com.

My idea is to add a name to the certificate and more users access the system will migrate Exchange 2013 email online (OWA, Outlook Anywhere, AS ...) by mail2.contoso.com.


Does this method is correct? something that has to be considered?

regards

---

Microsoft Certified IT Professional Server Administrator