Owing to the variety of possible charge and spin states and to the different ways of coupling to the environment, paramagnetic centres in wide band-gap semiconductors and insulators exhibit a strikingly rich spectrum of properties and functionalities
, exploited in commercial light emitters and proposed for applications in quantum information. Here we demonstrate, by combining synchrotron techniques with magnetic, optical and emph{ab initio} studies, that the codoping of GaN:Mn with Mg allows to control the Mn$^{n+}$ charge and spin state in the range $3le nle 5$ and $2ge Sge 1$. According to our results, this outstanding degree of tunability arises from the formation of hitherto concealed cation complexes Mn-Mg$_k$, where the number of ligands $k$ is pre-defined by fabrication conditions. The properties of these complexes allow to extend towards the infrared the already remarkable optical capabilities of nitrides, open to solotronics functionalities, and generally represent a fresh perspective for magnetic semiconductors.
