LM studio has a fork button on every chat part. Sorry, can't think of a better word - you can fork on any human or ai part. You can also edit, but editing isn't, it essentially creates a copy of the context with the edit, and sends the whole thing to the AI. This can overflow your context window, so it isn't recommended. Forking of course does the same thing, but it is obvious that it is doing so, whereas people are surprised to learn editing sends everything.