Can nuclear waste undergo fusion to turn it back into whatever it was before by using energy from renewables, thereby acting as a form of energy storage?
In practice, I don't think this would be at all viable, and certainly would not be competitive with other much more straightforward forms of energy storage.
Capturing all of the fission byproducts and reversing the process is going to be so technically difficult and energy costly that, in this context, it might as well be impossible.