I assume the new state would have a new index?
If so, it’s not easy to answer, as it would be comparable to an increased feature space for a linear layer.
The weight matrix does not contain valid parameters for this index yet, so you could e.g. extend the weight parameter and initialize the new parameters randomly.
We had similar discussions in this forum about adding new feature dimensions to a linear or conv layer and I’m not sure, what the best approach was (initializing the new parameters randomly or copying from existing parameters).