Yes. If open-sourced, we will be able to customize the model to our requirements. This is one of the most important modelling techniques called Transfer Learning
A pre-trained model, such as GPT-3, essentially takes care of massive amounts of hard-work for the developers: It teaches the model to do basic understanding of the problem and provide solutions in generic format.
With transfer learning, given that the pre-trained models can generate basic solutions, we can transfer the learning to another context.
This is the reason why GPT-3 has applications everywhere: Building chatbots, Q&A models, context inference, etc.
GPT-3 can understand the paragraph and generate generic summary. A custom GPT-3 would be able to understand medical journals and generate a subject relevant summary.