"Orthogonality" of chemical elements Chemical elements are said to be immutable at normal energies, but not at the energies that are orders of magnitude higher. 

Given that nucleus at normal energies gives us the Periodic Table and at higher energies becomes unstable, can we say that (with fusion) we will be able to transform an arbitrary chemical element into some other chemical element (if we have enough energy)?
Certainly nuclear fusion and nuclear fission can convert elements into other elements. Indeed, this is how different elements form in the first place.

The one issue I have is with your "arbitrary chemical element." You can use fusion to put together lighter nuclei or elements into heavier ones - up to iron, or use fission to divide more massive nuclei into lighter ones.. up to about iron.

The limit here is the binding energy of the nucleus which maximizes with $\ce{^{56}Fe}$.

In general, though, your point is a good one. Given enough energy (e.g., in a supernova), you can create lots of different elements.