You should create a separate manager for that, or clear the manager to destroy all objects. You can also also refresh each object in the list. But anyway that's expected behavior.
Create the object manager is very lightweight and you should usually create/destory manager frequently for small operations. There is no problem in creating many of them. Tables are not checked at all, db structure is only checked if you use TDatabaseManager and explicitly ask it to check for structure (ValidateDatabase or UpdateDatabase).