Training an ML model on two different datasets before using test data?

So I have the task of using a CNN for facial recognition. So I am using it for the classification of faces to different classes of people, each individual person being a it's own separate class. The training data I am given is very limited - I only have one image for each class. I have 100 classes (so I have 100 images in total, one image of each person). The approach I am using is transfer learning of the GoogLenet architecture. However, instead of just training the googLenet on the images of the people I have been given, I want to first train the googLenet on a separate larger set of different face images, so that by the time I train it on the data I have been given, my model has already learnt the features it needs to be able to classify faces generally. Does this make sense/will this work? Using Matlab, as of now, I have changed the fully connected layer and the classification layer to train it on the Yale Face database, which consists of 15 classes. I achieved a 91% validation accuracy using this database. Now I want to retrain this saved model on my provided data (100 classes with one image each). What would I have to do to this now saved model to be able to train it on this new dataset without losing the features it has learned from training it on the yale database? Do I just change the last fully connected and classification layer again and retrain? Will this be pointless and mean I just lose all of the progress from before? i.e will it make new weights from scratch or will it use the previously learned weights to train even better to my new dataset? Or should I train the model with my training data and the yale database all at once? I have a separate set of test data provided for me which I do not have the labels for, and this is what is used to test the final model on and give me my score/grade. Please help me understand if what I'm saying is viable or if it's nonsense, I'm confused so I would appreciate being pointed in the right direction.

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