We use a focussed laser beam to control the electronic activity of N- and H-atoms in a dilute nitride Ga(AsN)/GaAs quantum well. Our approach yields submicron resolution in the spatial manipulation of the electronic properties and can provide an alternative method to masking techniques for H-defect engineering and in-plane patterning of the band gap energy. This work was supported by the Royal Society and by the University of Nottingham, and the COST Action MP0805.