We propose a methodology | based on linear embedding via Green's operators (LEGO) and the eigencurrent expansion method (EEM) | for solving electromagnetic problems involving large 3-D structures comprised of ND ? 1 bodies. In particular, we address the circumstance when the electromagnetic properties or the shape of one body difier from those of the others. In real-life structures such a situation may be either the result of a thoughtful design process or the unwanted outcome of fabrication tolerances. In order to assess the sensitivity of physical observables to localized deviations from the \ideal structure, we follow a deterministic approach, i.e., we allow for a flnite number of difierent realizations of one of the bodies. Then, for each realization we formulate the problem with LEGO and we employ the EEM to determine the contribution of the ND i 1 \flxed bodies. Since the latter has to be computed only once, the overall procedure is indeed e-cient. As an example of application, we investigate the sensitivity of a 2-layer array of split-ring resonators with respect to the shape and the ofiset of one element in the array.