You don't need code really. All you need is the right prompt. GPT-4 should be well able to convert a description of the kind of personality and roleplay you're looking for into a suitable prompt for any LLM.

As programmers we're used to looking for ways to write code, but GPT-4 makes that unnecessary in many cases. Just look at these examples of casual conversation creating amazing outputs: https://www.youtube.com/watch?v=_njf22xx8BQ