In Autohex FA manager we restrict changing Tree items:
- Production year
- The engine type
- Model series
These 2 items will make a BIG difference when you change, 99.9999% you will be in a big mess after changing them.
In short: You cannot change the car model, because for sure you will be in a big problem.
The solution: Copy an FA from another car which is same model, engine, and year, after that you make the FA modifications.