As of now the Mean and StandardDeviation cannot be modified directly in the Deep Network Designer. A work around for this is to define that layer in the MATLAB Terminal and then import it into the Deep Network Designer.
To define the layer with Mean and StandardDeviation you can use the below code.
inputlayer = imageInputLayer([28 28 3],'Name','input','Normalization','zscore','Mean',ones(1,1,3),'StandardDeviation',ones(1,1,3))
Refer the below link for more information on defining the image input layer:https://www.mathworks.com/help/deeplearning/ref/nnet.cnn.layer.imageinputlayer.html
