Yes, and as you'd expect, this is how LLMs work today, in general, for control codes. But different elems use different control codes for different purposes, such as separating system prompt from user prompt.

But even if you tag inputs however your this is good, you can't force an LLM to it treat input type A as input type B, all you can do is try to weight against it! LLMs have no rules, only weights. Pre and post filters cam try to help, but they can't directly control the LLM text generation, they can only analyze and most inputs/output using their own heuristics.