Modify layer output in custom neural network

I want to modify the output of one layer before sending it to the next layer. As an example you can think of output a2(k) in the custom neural network in https://se.mathworks.com/help/nnet/ug/create-and-train-custom-neural-network-architectures.html. Is it possible to apply some function on it before sending to layer 3. Or else is it possible to apply a new input p3(k) at layer 3 whose elements depend on the value of a2(k)?