  Impurities embedded in electronic systems induce bound states which under
certain circumstances can hybridize and lead to impurity bands. Doping of
insulators with impurities has been identified as a promising route towards
engineering electronic topological states of matter. In this paper we show how
to realize tuneable Chern insulators starting from a three dimensional
topological insulator whose surface is gapped and intentionally doped with
magnetic impurities. The main advantage of the protocol is that it is robust,
and in particular not very sensitive to the impurity configuration. We
explicitly demonstrate this for a square lattice of impurities as well as a
random lattice. In both cases we show that it is possible to change the Chern
number of the system by one through manipulating its topological state. We also
discuss how this can be used to engineer circuits of edge channels.
