The aim of the present paper is to prove two perturbation theorems for selfadjoint operators/relations in Kreĭn spaces. As a matter of fact, these theorems represent generalizations of some results on the same topic, previously obtained by the second author. The authors consider that, in addition, those results are improved in the sense of involving more adequate hypotheses. Let \((H, [.,.])\) be a Kreĭn space and \(A\) be a selfadjoint definitizable operator, i.e., \([p(A)x, x]\geq 0\) for some polynomial \(p\). The real points of the spectrum \(\sigma(A)\) of such an operator can be classified into positive, negative and critical types. These sign types are essential in the spectral decompositions, which are one of the most important instruments of investigation. As generally in the context of perturbation theory, \(A\) is supposed to have some additional properties, e.g., boundedness, and the problem is whether \(A+ K\) preserves these properties, where \(K\) is a symmetric compact operator (perturbation). The authors stress two properties of this type, namely: (a) all spectral subspaces of \(A\) corresponding to compact subsets of \(\Delta\), which is open in \(\overline{\mathbb{R}}\), have finite rank of negativity, and (b) there exists a neighborhood of \(\infty\) such that the restriction of \(A\) to a spectral subspace corresponding to this neighborhood is a nonnegative operator.