I find it strange that you would need to restrict access to these tables based on Org/Site as these are administration application objects.
When you have two or more organisations using the same instance the configuration of the instance should be managed centrally to ensure the configuration complies with your central design and is tested across all organisations to check for conflicts.
Even if at some point you needed to move one of the organisations onto a new instance your configuration would need to be assessed and re-applied and then your org/site specific data migrated.
------------------------------
Steve Lee
Maximo Technical Sales Specialist
IBM
Leeds
------------------------------