@Gautam M Yes, you can create separate models for different invoice types and then create a composed model that can be used to predict different types of invoices. Please note the composed models can be created only when all the custom models are of a particular buildMode i.e template or a neural type. You cannot mix and match the models with different buildModes under one single composed model.
Building or Training on top of pre-trained model is currently not possible.
I hope this helps!!