Indeed, fine-tuning is still possible, but you can only go so far with fine-tuning before you need to completely retrain the model.
This is why Silo AI, for example, had to start from scratch to get better support for small European languages.
I was under the impression that you could still fine-tune the models or apply your own RLHF on top of them. My understanding is that the training data would mostly be useful for training the model yourself from scratch (possibly after modifying the training data), which would be extremely expensive and out of reach for most people