You don't need to change many weights, relatively, to add capabilities or modify behavior. Look up LoRas for instance.
I'm of the opinion that post-training existing models is an area with a lot of benefit and fun in the near future (it's already being done here and there of course).
I doubt you _really_ have to know everything in this course to know how to do that, but I'd want this as background personally for it.
You also don’t have to go straight into LLMs. You can learn most of the training mechanics via classic deep learning. It isn’t much different with LLMs except the training data and losses are specific and the models are much larger.