1 - It helps to add your state, laws vary.
2 - Generally, aftermarket computers are non-engineerable (you cannot prove the engine meets emission standards).
3 - Speak to an engineer to get a proper opinion. In Vic you can get a list of them from Vicroads.
4 - I think the short answer will be no. Long answer will be a yes if you have deep pockets and REALLY want to.
Hen