  This paper is devoted to the study of preservation of eigenvalues, Jordan
structure and complementary invariant subspaces of structured matrices under
structured perturbations. Perturbations and structure-preserving perturbations
are determined such that a perturbed matrix reproduces a given subspace as an
invariant subspace and preserves a pair of complementary invariant subspaces of
the unperturbed matrix. These results are further utilized to obtain
structure-preserving perturbations which modify certain eigenvalues of a given
structured matrix and reproduce a set of desired eigenvalues while keeping the
Jordan chains unchanged. Moreover, a no spillover structured perturbation of a
structured matrix is obtained whose rank is equal to the number of eigenvalues
(including multiplicities) which are modified, and in addition, preserves the
rest of the eigenvalues and the corresponding Jordan chains which need not be
known. The specific structured matrices considered in this paper form Jordan
and Lie algebra corresponding to an orthosymmetric scalar product.
