OCS R2 does introduce new schema classes and attributes to accommodate for some of the new roles. So a schema update is required to deploy OCS R2 regardless if you have prepped for OCS RTM or not. Here are list of the Classes that are new (this is not a full list of classes):
msRTCSIP-ApplicationServer - holds entry for SCP for UC Application Server (UCAS)
msRTCSIP-ApplicationServerService - class provides an association from a specific pool to its application server
msRTCSIP-ApplicationServerSettings - aux class to msRTCSIP-Application Server holds attributes for application servers
msRTCSIP-ConferenceDirectories - class is a container for multiple instances of conference directories and doesn't contain any attributes itself
msRTCSIP-ConferenceDirectory - this class holds attributes representing settings for a specific conference directory
msRTCSIP-DefaultCWABank - aux class holds settings for CWA bank.
msRTCSIP-LocationContactMapping - class is created by conference auto attendant (CAA) and holds attributes used to categorize conference numbers by region
msRTCSIP-LocationContactMappings - class is container for multiple contact mappings. Doesn't hold attributes itself.
msRTCSIP-MonitoringServer - class hold attributes that represent settings for a single monitor server.
These are the ones that I've seen so far. I'll publish the link to the Active Directory OCS R2 Reference document when it's published.
Keep in mind that the schema prep is run once against the schema master for each AD Forest where you plan to deploy OCS Servers. In a resource forest then run in the resource forest not the user forest. In a central forest run only on central forest not in user forest.
So for the installation it's similar to past installs with schema prep, forest prep, and domain prep. The forest prep creates global settings and universal groups that are used by OCS, and domain prep adds permissions on objects to be used by members of universal groups.