co-existence exchange 2003 and 2010

I am using the Exchange Deployment Assistant for migrating to Exchange 2010, next to Exchange 2003. I have installed two CAS servers of 2010 and created a CAS Array, using NLB on these Windows 2012 Servers. The internal name is CASLB, the name of the CAS servers are CAS1 and CAS2. 

Now I am the point in the assistant, where it says "Configure OAB and WEB services virtual directories". The command is :

set-OABvirtualdirectory -Identity "CAS1\OAB (Default Web Site)" -ExternalUrl https://mail.contoso.com/OAB -RequireSSL:$true

and a similar command for Web Services

Since I do not want the OAB in Exchange 2003 to be stop working, can really execute this command already? And secondly, can I change CAS1 here to CASLB, so with my loadbalancer/CAS Array name? And do I need to execute this command on both CAS servers? 

Thanks in advance!