  Assume that $M(\mathcal{T})$ is a rational homology sphere plumbed 3-manifold
associated with a connected negative definite graph $\mathcal{T}$. We consider
the combinatorial multivariable Poincar\'e series associated with $\mathcal{T}$
and its counting functions, which encode rich topological information. Using
the `periodic constant' of the series (with reduced variables) we prove surgery
formulae for the normalized Seiberg-Witten invariants: the periodic constant
appears as the difference of the Seiberg-Witten invariants associated with
$M(\mathcal{T})$ and $M(\mathcal{T}\setminus\mathcal{I})$, where $\mathcal{I}$
is an arbitrary subset of the set of vertices of $\mathcal{T}$.
