Yes, it can be done. To simulate a false data injection attack, one can modify the payload or the header of a network packet to change the data that is being transmitted. The below link has a useful technical guide that explains step-by-step how to set up an FDI attack in NetSim - https://www.tetcos.com/pdf/v13.3/False-Data-Injection-Attack_NetSim-v13.3.pdf