Reprogramming (reconfiguring) software running on the nodes of a WSN (Wireless Sensor Networks) is needed to update or add new functionalities or fix existing bugs. Reducing the amount of data sent to the node via the radio interface means reducing the energy consumed by the sender and receiver nodes, enabling them to run for longer. We present a solution for performing such functionality exchanges on different node hardware, each running under different operating systems. The universality of our solution is based upon the semantics of a high-level language called MinTax which is compiled in-situ, on the node itself. In order to validate the feasibility of a hardware-software heterogeneous WSN, we present the case of a functionality sent between two different hardware nodes, one running ContikiOS and the other, FunkOS.