Earlier quoted context omitted.
Add "Always use dash instead of em dash" to the developer/system prompt, and that's never an "issue" anymore. Seems people forget LLMs are really just programmable (sometimes inaccurate) computers. Whatever you can come up with a signal, someone can come up with an instruction to remove.
That doesn't work, they beat it so hard into ChatGPT it won't always listen to you about it. You can't stop it from doing the "if you like I can " thing in every reply either.
I don't think you're able to set either the developer or system prompt on ChatGPT, you're gonna have to use the OpenAPI (or something else) to be able to set that. Once you have access to setting text in those, you can better steer how the responses are.