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To be able to transform an instance in Studio (move, rotate or scale), you have to use the Instances Selection Mode (on the main tool bar). In this mode you can select only instances in the viewport and transform them using the transform gizmos, or select from the Instances list and then transform them.
The Instances Selection Mode (right most icon)
Assigning materials to instances
At first an instance will inherit the material from the original object, but you can assign any other material to each instance you create, by simply dragging a material from the Materials List over the instance.
It is also possible to remove material assignments in instances by selecting the material in the Instances List and clicking the “Del” key. In absence of any assigned material, an instance by default will inherit the material of its original object.