This is a subject I've seen but never had the budget to try. I can tell you that I know one painter who does this but won't tell me what parts he swapped out.
There are painters all over the world that use mis-matched needles and nozzles, on purpose. It gives a different paint response curve do to the different angles between the needle and nozzle. Search ab forums, you'll find a ton of set-ups people have found through trial and error. One I have seen is: On Iwata HP-Cs The 0.3 tip is replaced with a 0.2 tip from an HP-B, leave the 0.3 needle(the 0.3 needle fits the 0.2 tip), and the original 0.3 aircap has more airflow than the 0.2 aircap so between the angle difference and the extra airflow you end up with finer spray patterns.
Again, this is all second hand info...take it for what it's worth. And it's going in the opposite direction size-wise as far as your original question goes.