A method is proposed to control the aspect ratio (epsilon) of elongated nanoparticles obtained by ion implantation in a transparent matrix. The procedure was tested for Ag spheroids in silica and we could accurately change epsilon in the range from the maximum value obtained by the ion implantation (around 3.0 in this case) to 1.0 (spherical shape). The values of epsilon were determined in several steps from optical extinction spectroscopy measurements, by fitting the modification and splitting of the surface plasmon resonance peak, using the T-matrix method. In the initial (maximum deformation) and final (undeformed) states, transmission electron microscopy images were obtained, showing a good agreement with the T-matrix results in both cases.