This work presents a unique role played by swift heavy ion irradiation (SHI) on Co3O4 - reduced graphene oxide (RGO) nanocomposites in modifying its optical, magnetic and surface electronic properties. On exposure to SHI, there occur delinking of the attached functional groups from RGO thus driving towards its purification. Raman spectra of irradiated samples confirm this result, where, an exponential decrease in the intensity ratio of D and G peaks of RGO with fluence occurs. At the same time, SHI generates extended defects in the form of latent tracks in decorated Co3O4 nanoparticles, thus modifying the magnetic and surface electronic properties. Results obtained from magnetization studies using SQUID magnetometer and surface electronic response from scanning Kelvin probe reveals that a linear relationship could be established between magnetization and work function of the nanocomposite. An estimation for variation of defect-induced damage fraction with fluence is made from measured work function values.