  We consider accelerated black hole horizons with and without defects. These
horizons appear in the $C$-metric solution to Einstein equations and in its
generalization to the case where external fields are present. These solutions
realize a variety of physical processes, from the decay of a cosmic string by a
black hole pair nucleation to the creation of a black hole pair by an external
electromagnetic field. Here, we show that such geometries exhibit an infinite
set of symmetries in their near horizon region, generalizing in this way
previous results for smooth isolated horizons. By considering the limit close
to both the black hole and the acceleration horizons, we show that a sensible
set of asymptotic boundary conditions gets preserved by supertranslation and
superrotation transformations. By acting on the geometry with such
transformations, we derive the superrotated, supertranslated version of the
$C$-metric and compute the associated conserved charges.
