  Formulas previously presented for the Casson-Walker invariant are generalized
to Lescop's extension. These formulas in terms of linking numbers and surgery
coefficients compute the change in Lescop's invariant under crossing changes in
a framed link presenting a 3-manifold. This leads us to revisit an old formula
for a coefficient of the Conway polynomial. Finally we compute Lescop's
invariant of several lens spaces and deduce some values for Dedekind sums.
