https://raw.githubusercontent.com/0xeb/TheBigPromptLibrary/r...

I think this is pretty much the entirety of study mode. Never used it before but as long as there's no UI changes, yes, it's 100% replicable.

There used to be a “Custom GPT” feature which basically just creates a prompt wrapper with some extra functionality like being able to call web APIs for more data. Can’t seem to find that menu right now, but it would have easily replicated the study feature. Maybe it was limited to paid accounts only.