Henselian Schemes

I have a question about properties of Henselian ring/schemes exploited in M. Artin's article "On Isolated Rational Singularities of Surfaces":

Here the relevant excerpt:

In the excerpt we start with schemes $$V, \bar{V}=Spec(A)$$ where $$A$$ is a local, normal $$2$$-dimensional ring with algebraically closed residue field $$k$$.

Let futhermore $$\pi:V \to \bar{V}$$ be birational proper map with $$V$$ regular, i.e. a "resolution" of the singularity of $$\bar{V}$$.

Denote by $$Z= \sum_i X_i$$ the fundamental cycle; here the definition:

$$Z$$ is noting but the unique smallest cycle satisfying property (ii)

In order to verify $$V \times_{\bar{V}} Spec(A/m^n)= nZ$$ the author firstly replaces $$A$$ by it's henselisation $$A_h$$.

(1) My first question: Why this replacement can here be done wlog?

And my second question is:

Above in the excerpt the author claims that since $$A$$ is henselian (after replacing $$A$$ by $$A_h$$) one always can find a divisor $$D$$ with following essential property on intersection numbers

$$(D \cdot X_i) = - (Z \cdot X_i)$$.

(2) My second question is simply why the henselian property allows to find such divisor $$D$$?