Overriding instance attributes

Separate from nesting an instance inside its own transformation node, is it possible to specify attribute values for a specific instance that are different from the library item’s values?

For example, modified from an example in the spec:

<library type="LIGHT">
  <light id="sun" name="the-sun" type="DIRECTIONAL">
    <param name="COLOR" type="float3">1.0 1.0 1.0</param>
  </light>
</library>
<scene>
  <node>
    <instance url="#sun" />
    <instance url="#sun" name="the-moon">
      <param name="COLOR" type="float3">0.8 0.9 1.0</param>
    </instance>
  </node>
</scene>

(In case it’s not clear, the intent is to re-use attributes for each instance, but be able to specify per-instance changes in a sparse manner.)

Possible?

The <instance> element will support some per-instance data beginning with the 1.4.0 schema to be released Oct 28th. This includes rebinding animation, materials, rigid body and geometry specifically. In addition, the <extra> element will be allowed as a child element and that will enable rebinding of <param> elements.