  In the exact renormalization group (RG) flow in the infrared cutoff $\Lambda$
one needs boundary conditions. In a previous paper on $SU(2)$ Yang-Mills theory
we proposed to use the nine physical relevant couplings of the effective action
as boundary conditions at the physical point $\Lambda=0$ (these couplings are
defined at some non-vanishing subtraction point $\mu \ne 0$). In this paper we
show perturbatively that it is possible to appropriately fix these couplings in
such a way that the full set of Slavnov-Taylor (ST) identities are satisfied.
Three couplings are given by the vector and ghost wave function normalization
and the three vector coupling at the subtraction point; three of the remaining
six are vanishing (\eg the vector mass) and the others are expressed by
irrelevant vertices evaluated at the subtraction point. We follow the method
used by Becchi to prove ST identities in the RG framework. There the boundary
conditions are given at a non-physical point $\Lambda=\Lambda' \ne 0$, so that
one avoids the need of a non-vanishing subtraction point.
