Blender gives you a mesh that isn't parameterized. Not particularly useful for making dimensional changes outside of eyeballing everything. An LLM isn't going to reliably hit your dimension targets so tweaks will be necessary.
If you just need to tweak the dimensions in the script, or are satisfied with describing the changes to the LLM and having it modify the script, there isn't much difference in practice between a generated OpenSCAD script and a Blender python script.