This is one of those classic LLM scenarios that doesn't make sense.
If you can tweak the model in a CAD package, you can quite possibly make it in CAD in the first place more quickly than you can manage several rounds of descriptions with an LLM.
It's like the whole "I'd like to get an LLM to write a song and then I'd adjust it" thing. No musician needs this. If you can truly fine-tune a song, writing one is easy. And if you aren't a musician, you won't get good results fine-tuning a song.
If you can tweak the model in a CAD package, you can quite possibly make it in CAD in the first place more quickly than you can manage several rounds of descriptions with an LLM.
It's like the whole "I'd like to get an LLM to write a song and then I'd adjust it" thing. No musician needs this. If you can truly fine-tune a song, writing one is easy. And if you aren't a musician, you won't get good results fine-tuning a song.