For the bias point concept .. it is assumed that
the signal amplitude is very very small , that is
when we call it a small signal operation .. but
when a large signal is applied the diode operating
point is bound to change .
I am not sure what you mean by bias point, but if a diode is fast enough to respond to a microwave signal, it will rectify that AC signal into a DC current/voltage. That will change the DC bias setup.
In an RF switch with PIN diodes, you want the I region of the diode thick enough so that does not happen, for instance.