We report on calculations of the ballistic thermal conductance of nanowires with modulated width along their length. We discuss the effect of the shape of the modulation in the thermal conductance of the nanowires. The ballistic thermal conductance is determined by the phonon transmission coefficient. It is shown that the thermal conductance of the modulated wires is lower than that of the corresponding straight wires. The phonon conductance decreases with increasing number of modulating periods and saturates to the infinite superlattice value. It decreases below this value when the modulation profile is non-periodic. It is shown that the thermal conductance can be tuned by changing the shape of the modulation profile. This behavior could lead to structures of nanowires with enhanced thermoelectric efficiency.