  We prove an additivity property for the normalized Seiberg-Witten invariants
with respect to the universal abelian cover of those 3-manifolds, which are
obtained via negative rational Dehn surgeries along connected sum of algebraic
knots. Although the statement is purely topological, we use the theory of
complex singularities in several steps of the proof.
  This topological covering additivity property can be compared with certain
analytic properties of normal surface singularities, especially with functorial
behaviour of the (equivariant) geometric genus of singularities. We present
several examples in order to find the validity limits of the proved property,
one of them shows that the covering additivity property is not true for
negative definite plumbed 3-manifolds in general.
