It can, sometimes I have seen a better milage after modification but I can not realy tell what will help, in my early days with a small change in crank timing (1 degree both ways) I have seen some results but todays top engines are much larger timed.
I believe de pipes you can get are optimized to work with the factory team engines and so they do perform a little bit less with "standard" engines, getting the right pipe (and that could be one from another brand) can give more result. To give an example, the 2052 on a JP Eagle did give me 4:45 maximum while a 2013 can give me 5:30 on the same engine.

Current Flash engines in combination with a Novarossi pipe are not easy to get 5 minutes. These engines are made to get as much mixture in and to get all the combustion out. Over here the 2013 is not alowed in racing so I can not tell how it performs on current engines.