Not very necessary. An LLMs Brain might be static itself but the connections it makes between neurons are very much dynamic. That's why in context learning is possible. LLMs already mimic meta learning and fine-tuning when you few shot.

https://arxiv.org/abs/2212.10559#:~:text=Language%20Models%20Secretly%20Perform%20Gradient%20Descent%20as%20Meta%20Optimizers,-Damai%20Dai%2C%20Yutao&text=Abstract%3A%20Large%20pretrained%20language%20models,Context%20Learning%20(ICL)%20ability.