A procedure aimed to support designers in achieving structural improvements to reduce the seismic vulnerability of an electrical network is presented. This method based on the use of ASK4ELP software (Assessment of Seismic Risk for Electric Power Grids) allows minimising the costs of the actions needed in order to reach the required level of reliability, as defined by two different indexes of damage, namely the loss of transmitted power and the number of customers excluded from the service. An updating plan for the reinforcement of a power transmission grid includes the identification of its critical nodes, of the electromechanical components to be strengthened and of the related reinforcement level. In this paper, it is shown how the vulnerability assessment carried out with ASK4ELP can help in finding the optimal solution to these tasks, increasing the effectiveness-to-costs ratio. Three different empirical criteria for the individuation of the critical nodes are evaluated and the simulation of a significant part of the Italian transmission grid is presented: the results suggest that the most effective criterion for individuating the grid critical nodes should be given in terms of their exclusion probability.