Can a derivative of non-open-source AI be considered Open Source AI?

Regarding point 1, I’m not sure to what extent fine-tuning is possible. However, I do believe a considerable amount of adjustment is possible. It would be better to ask AI vendors about this.

My understanding is that in fine-tuning, the weights of the newly added layers with trainable weights are updated along with the weights of the layers of the pre-trained model. However, not all layers of the pre-trained model are updated. If all layers were updated, it would negate the purpose of having a pre-trained model in the first place.