Create a custom dnn which incorporate pretrained alexnet and linear regression model

hi I use the activation feature from pretrained alexnet to train linear regression model. And now I need to create a custom deep neural network which would incoporate the pretrained alexnet and linear regression model and also a fully connected layer. Can anybody tell me how to realize that?

The finetuning tutorial might be a good starter, as it explains how to modify pre-trained torchvision models for a custom task and fine tune them.