  For a digraph D and three parameters x, y, z in {0,1,+,-} we define the
digraph D^(x,y,z) and call it the (x,y,z)-transformation of D. We show that for
every r-regular digraph D the adjacency characteristic polynomial A(t,
D^(x,y,z)) of (x,y,z)-transformation of D is uniquely defined by r and the
adjacency characteristic polynomial A(t, D) of digraph D and we give a
description of this function A(t, D^(x,y,z)) = F(r, A(t, D)). We also obtain
similar results for some non-regular digraphs, namely, for so-called
digraph-functions and their inverse. Also using the (x,y,z)-transformations of
digraphs, we give various new constructions of non-isomorphic adjacency
cospectral digraphs.
