Could the comparison of two values in time domain converted into frequency domain?

My question is based on a mass-spring-damper system. For example in time domain when the output x(t) is greater than 5m, the stiffness k will change into another function. Is it possible that the following case is realized in simulink?

[Birdman]

Can you share your model?

Answer 1

[FENGPEI YUAN]

This is the basic Simulink model. But there is some problem with the part of 'MATLAB function block', including the input and function. Here is the function:

     function y = fcn(u1,u2)
  % u1 -- Theta(s)
  % u2 -- the reference(comparison) point
     refer = u2.*pi;
     k_initial = 0.64;
     if u1 <= refer
         y = k_initial .* u1;
     else
         y = k_initial.*u1.*exp(-i.*0.2);
     end
     y = real(y);

As you can see, what I want is to realize the case in the frequency domain that the value of k will be changed into another expression when the output theta(t)> threshold in time domain.

Thanks!