Sorry, what you proposed is already taken into account. This Luxury Tax thing is just another layer of unnecessary layer of bureaucracy.
Luxury Tax Link on government website . It clearly specifies that if you buy a good that is under the luxury tax but then you add modifications that push it over, you have to self-report and then pay the tax. Your modifications will be registered and knowing the government, they'll probably penalize you as well. I would suggest everyone read the technical document and not to take things at face value.
This is insanity! Without getting too political I understand the why the government think its needed given that there's a massive fiscal deficit, but I have hard time seeing this implementation be anything but costly. I think the government incorrectly assumes that the rates of sales of luxury items will continue despite this tax and then adds on a 10% tax to assume tax revenue. There is price sensitivity, and I am fairly certain that this scheme will bring in less money than they've outlined. Not to mention they didn't index anything to inflation, so eventually, more cars move into the luxury goods category lets say 20 years down the line.
I'm also sick of all these pay your fair share because you have nicer things. I work hard, save up, and I feel like I get penalized all the time while others spend like drunken sailors. I do well and I consider myself upper middle class, but I'm hardly living an extravagant life of luxury. The simplest thing the government can do to make tax revenue is just to add more income tax brackets above the current ones. It's easy to do, you can reassess the brackets yearly, and it doesn't cost anything extra to implement. Instead, we get another added tax that's poorly thought out because it sounds good, but will be extremely hard to remove once it's enacted. Remember the income tax? That was implemented to help pay for the costs of fighting World War 2. All we get is a hollowing out of the middle class while the ultra-rich puppet masters laugh away.
/end rant