Comment by Der_Einzige

API driven LLMs on purpose don't implement core features which would enable which you want, for example, negative prompting.

You can negative prompt any LLM with stuff like "always write the word interesting in your response".

You can also use techniques for modifying logprobs of tokens, which is avaialble in gpt-4 api (but is hard to use). You can literally ban "interesting" from its vocabulary.

You could even use representation steering techniques to do this using control vectors. See this library as an example: https://github.com/Hellisotherpeople/llm_steer-oobabooga