Migration from 2003 to 2010. Question about legacy LDAP recipient policy

Hello everyone, 

I'm migrating from Exchange 2003 multi-administrative group organization to Exchange 2010. There are about 100 recipient policies from 2003 one for each Admin Group in the Organization.

One of these Recipient Policies, uses the following LDAP Filter  

"(&(mailNickname=*)(legacyExchangeDN=/o=Catal3/ou=GR-AG/*))"

my plan is :

1. moving all mailboxes from 2003 in GR-AG Administrative Group to 2010,

2. AFTER decommissioning all Exchange 2003 in GR-AG (completely uninstalling them), converting the Recipient Policy with OPATH syntax.

My problem (well...actually "my doubt") is: do I have to delete the Recipient Policy and create corresponding Email Address Policy back with the new syntax *OR* can I convert directly the Recipient Policy to Email Address Policy and contextually change the LDAP filter to OPATH syntax?

In such case, there is a chance to disrupt in other AGs? 

Thanks!