The injection of tunneling electrons from tips of scanning tunneling microscopes (STM) to crystalline C-60 films induces a change in STM images indicative of polymerization of the clusters, the efficiency of which is strongly affected by the internal strain in the film [Y. Nakamura et al., Appl. Phys. Lett., 77 2834 (2000)]. The tip-induced polymerization effect in films deposited on Si substrates spreads spatially over similar to10 nm from the electron injection point. However, the extent of the spread is reduced in films grown on graphite substrates presumably due to a difference in the intercluster spacing.