Muon-catalyzed nuclear fusion works on D-D, D-T, and D-He3 fusion by the muon orbiting much closer than an electron, enabling the nuclei to get much close to each other than they normally would. Tau-catalyzed fusion also works like that, but would be even better.
One has to replace every electron in an atom by a muon to make this work, and it is much easier on a hydrogen isotope than on any other element's isotopes. For that reason, muons are not any help in making superheavy elements -- too much charge to cancel out.
For a hydrogen atom, the effective radius is the Bohr radius, about 5.29*10^(-11) m. Doing these calculations for an infinitely massive nucleus, a muon is about 200 times more massive, making its effective orbit radius about 2.56*10^(-13) m. A tau lepton is about 4000 times more massive, making its effective orbit radius about 1.52*10^(-14) m. A tau lepton is about as massive as a deuterium nucleus, making the combination's reduced mass twice as large, giving an effective orbit radius of about 3.11*10^(-14) m.
Tau leptons have a big deal breaker, however, their lifetime. A muon has a mean life of 2.197*10^(-6) seconds, and a tau a mean life of 2.903*10^(-13) s. Multiplying both lifetimes by c gives 659 m for the muon and 87.0 micrometers for the tau. So a tau will not last long enough to do much catalysis.