The capability of hydrogen to passivate nitrogen in dilute nitrides is exploited to in-plane engineer the electronic properties of Ga (AsN)/GaAs heterostructures. Two methods are presented: i) by deposition of hydrogen-opaque metallic masks on Ga (AsN) and subsequent hydrogen irradiation, we artificially create zones of the crystal having the band gap of untreated Ga (AsN) surrounded by GaAs-like barriers; ii) by employing an intense (~ 100 nA) and narrow (~ 100 nm) beam of electrons, we dissociate the complexes formed by N and H in a spatially delimited part of a hydrogenated Ga (AsN) sample. As a consequence, in the spatial regions irradiated by the electron beam, hydrogenated Ga (AsN) recovers the smaller energy gap it had before hydrogen implantation.