Yeah, if you first click the object in the project tree on the right, then go changing things in behavior properties, they will be applied to all the objects. Also newly created.
When you put an instance on the layout, and click that first, and then change properties, you will change the properties for that object instance in the layout. And newly created objects will have the ones from the default values in the project tree.
You can double check, because, after you give one instance a new value in the layout, then click the same object again in the project tree, you will notice the property has gone blank, indicating at least one instances exist with varying values.
would you now change the behavior value from the one in the project tree, the ones in the layout will receive the same value ...