Not only illegal, your kidding yourself that a cop won't realise what you've done. Sell your atomik and keep the motovert. At the very least you can use everything from your atomik but the frame. First thing any cop will do is check for the compliance plate on the frame of a bike that looks like a pitbike with lights slapped on it. Don't think about swapping the comp plate from one frame to another and restamping frame numbers to suit, it'll end up in you not only getting the bike taken away but the fines are more than what a motovert rx costs.
If you plan on buying a motovert anyway why bother trying to pull a dodgy bait and switch, the motovert will not be worth much if you try to sell it without its comp plate, if you plan on selling it with the comp plate you will almost certainly get busted as soon as the next owner tries to rego it. Like i said, buy the motovert, build your atomik onto the rx frame if you want, should only take a weekend at most and sell off the leftover bike. You probably didnt want to hear it but you can't really expect to propose something like this on a public forum and expect people to encourage you