I am saying that a nonlinear transfer function generates intermodulation distortion when applied to complex signals - not harmonic distortion. For sure, you can have any transfer function you want using DSP, but it won't be meaningful when applied to a complex signal.
Can you please explain why a physical device with a non-linear transfer function does not produce the same intermodulation effects? And if I can simulate the same transfer function as some physical device in DSP, why would this not be meaningful?