As long as you are running baffels in the slip on's you should be fine. You might want to check your spark plugs after about 120 miles or even a tank of gas and see if they look OK. If you take them out and look at them before you ride, while engine is cold and then check them after a few rides and see if there are any changes. I like to check them cold they are easier to handle and in my opinion less chance of cross threading them when you replace them.If you aren't sure on how to read them, there are some post on it. Also it is a little more difficult to read them with the new fuels nowaday's. You could always take them to your dealer and let one of the tech's look at them.
I check mine every 500 miles or so just to keep tabs on them. If you notice any driveability issues after changing your pipes, I would definitley have someone check it out. Otherwise you should be fine.