Yes we don't have emissions testing anymore. But removing the cat or any emissions component is still against the law and punishable by a stiff fine. It may even be a felony but I cannot confirm that. I don't care much about laws or being regulated. I am just letting you know.
We may be different here in MN, haven't checked here, but in the other states I lived in it was illegal for certified mechanics to remove them from anyone else's vehicle, but the owner was perfectly within their rights to remove their own cats. Had something to do with the freedom to use your own vehicle the way you saw fit if you had the knowledge to accomplish it but still wanting to disuade just anyone for having them removed for no reason or just to save a little dough when repairs were needed. Again, MN may have outlawed any removal and you should check first.
The way I look at it is what they don't know can't hurt them. I have been pulled over before in the communist city of Minneapolis in my 78. The Officer asked if there were any emmissions components removed or something like that. I just told him, "Not to my Knowledge." I think he was just being a bully. I also had the teller ask me the same thing when transferring a vehicle title as well. My reply was exactly the same regardless. Its private property, and I honestly don't think it is any of their business.
I've heard of some people knocking the guts out, and putting it back up. The flaw with that is then you will hear a howling noise. I've also heard of some putting a straight pipe inside of the cat to eliminate the howling.