You can do what you want but you need to understand the repercussions. They can go back years and collect sales tax on past sales if they catch you. The best thing to do is make a date and start doing it the correct way. That way if they do catch you then you have a direct point where you can say you found out and corrected your mistakes.
Your current questions should be gone past a CPA or start reading at the WI DOR. Either way you need to fix it and it's better sooner than later.