Finally someone else using ASTs while working with LLMs and modifying code! This is such an under-utilized area. I am also doing this with good results: https://codeplusequalsai.com/static/blog/prompting_llms_to_m...
https://arxiv.org/pdf/2405.15793
It uses smart feedback to fix the code when LLMs occasionally do hiccups with the code. You could also have a "supervisor LLM" that asserts that the resulting code matches the specification, and gives feedback if it doesn't.