You can with out a tune, you'll throw a cel all the time though. Mostly, the rear 4 pin o2 is what is a pain, they just dont get enough of a temp differential and dont see a big enough drop in emissions from the front ( 6 pin wideband ) . I ran 17/8 LT and high flow cats for about a year. CEL came and went but it was a pain. You can do it though, its not going to blow the car up, it'll sound nicer. But a tune should really be done.
Now though with all the EPA stuff, most shops dont turn off the rear o2. Its not hard to turn that check off though via a tuner. BUT.. if you have to emissions test your car, those disabled checks will cause you to fail. So, you end up chasing the CEL. I could make it a month or two. It would always pop though after a hard pull.