Why you need to manipulate it in numpy?
You can always create your custom layer or lambda layer:

  
      

      keras.io
  

  
    

Keras documentation: Making new layers and models via subclassing 1



  

  
    
    
  

  



  
      

      keras.io
  

  
    

Keras documentation: Lambda layer 1



  

  
    
    
  

  


If you want we have also a numpy API in TF:

  
      

      TensorFlow
  

  
    

NumPy API on TensorFlow  |  TensorFlow Core 2