You can do that by modifying corresponding line on that link.
For example, if you want to change all the relu in the model architecture into elu,
replace nn.ReLU in line 31, 34, 50, 70, 72 of https://github.com/pytorch/vision/blob/master/torchvision/models/vgg.py 184 to elu, then call the vggXX function to make model instance