Yes, I do believe that you can. A lot of people erroneously think they can just bolt on canisters with no effect on air/fuel. I have dynoed many bikes in over ten years . . . what some people don't realize is that these bikes are leaned on hard - air/fuel wise - in order to pass the EPA requirements in this country. Clean air systems (like the PAIR valve) were introduced to help battle this problem as far back as 1979. The advent of fuel injection helped the OEMs make their bikes comply. Anyone who has actually put a bike on a dyno and put an air/fuel probe into the pipe knows exactly what I am talking about. They are lean to start with - right from the factory. Then you go and install slip ons. They then become borderline worse - they usually run okay, and most customers are too dumb to think anything is wrong. Sometimes decel popping occurs, and a light goes on.
Yes, you can get some improvements by tweaking the air/fuel, either with a powercommander, ECU editor, or whatever else your local shop might be pushing . . . either way, it is worth it, just the improved throttle response alone makes it worthwhile - and knowing your air/fuel is right.