Well, Bob - this would depend on which isotopes of Ni are involved, as some reaction could be gainful - but one thing that almost every expert agrees on, is that if-and-when Nickel does transmute to Copper, one cannot end-up with a natural copper isotope ratio as the ash.
Moreover, there will be some percentage of radioactive species (copper or otherwise) with detectably long half-life (months to years) - and these will be extraordinarily easy to document if they are present. The reason that these isotopes have not been documented (by the Swedes, for instance) can most likely be attributed to the fact that nickel is NOT transmuting into copper (or anything else) for most of the gain in this reaction. They would have detected tritium or almost any other radioactive isotope, if present - since they had access to the unshielded spent-fuel from Rossi to test. From: Bob Higgins Peter Hagelstein says that transmutation of nickel to copper is overall endothermic. If you want to show the heat came from the transmutation - that is a far different story, and Piantelli or no one else has come close to a correlation of the heat radiated to the tiny amount of transmutation.
