Control of electron spins in individual magnetically doped semiconductor nanostructures has considerable potential for quantum information processing and storage. The manipulations of dilute magnetic interactions have largely been restricted to low temperatures, limiting their potential technological applications. Among the systems predicted to be ferromagnetic above room temperature, Mn-doped GaN has attracted particular attention, due to its attractive optical and electrical properties. However, the experimental data have been inconsistent, and the origin of the magnetic interactions remains unclear. Furthermore, there has been no demonstration of tuning the dopant exchange interactions within a single nanostructure, which is necessary for the design of nanoscale spin-electronic (spintronic) devices. Here we directly show for the first time intrinsic magnetization of manganese dopants in individual gallium nitride nanowires (NWs) at room temperature. Using high-resolution circularly polarized X-ray microscopy imaging, we demonstrate the dependence of the manganese exchange interactions on the NW orientation with respect to the external magnetic field. The crystalline anisotropy allows for the control of dilute magnetization in a single NW and the application of bottom-up approaches, such as in situ nanowire growth control or targeted positioning of individual NWs, for the design of networks for quantum information technologies.