This is a concern of mine, as well as limiting the amount that an LLM can talk through a problem - sometimes to nothing. Getting them to work through things IMO dramatically improves their output.
My gut feeling is that taking the output and if it's broken then start fixing it would have a better result - you could even then completely limit the output to only valid json. For your example, if it wrote "very_healthy" and was given an error message explaining that this wasn't an option it had to choose from very_unhealthy" or "moderately_healthy" I would expect a halfway decent model to pick "moderately_healthy".
This has the benefit of allowing you to use a more powerful model for reasoning (like GPT4) and a local model where you can do this kind of token probability manipulation for just fixing the data.
My gut feeling is that taking the output and if it's broken then start fixing it would have a better result - you could even then completely limit the output to only valid json. For your example, if it wrote "very_healthy" and was given an error message explaining that this wasn't an option it had to choose from very_unhealthy" or "moderately_healthy" I would expect a halfway decent model to pick "moderately_healthy".
This has the benefit of allowing you to use a more powerful model for reasoning (like GPT4) and a local model where you can do this kind of token probability manipulation for just fixing the data.