A new frontier in tuning the electromagnetic response of carbon-based materials, particularly carbon nanotubes, consists in adding metallic clusters or nanoparticles at their external surface. This allows to change optical, dielectric and magnetic properties with potential applications in electronics and telecommunications for aeronautics. By resorting to first principles dynamical simulations, we provide a microscopic picture of the interaction at finite temperature between a carbon nanotube and Co aggregates mimicking the experimental coverage. The electronic structure evolution provides the absorption spectrum and the dielectric function for comparison with experiments and guidelines for tuning these composite systems.