By disassembly do you mean removal of the nib & feed? It's a simple friction fit feed. It pulls right out, not terribly different from a Metropolitan.
However - I was warned to avoid TWISTING when removing the nib and feed. Apparently there an internal piece that has a chance of twisting out which you don't want... So grip gently but firmly, taking care not to bend the nib or feed's slits -- and pull straight out.
I have 3 Pilot Custom 91s and all of them arrived writing a bit too dry. I removed the nib and feed in each for some gentle flossing and very very very subtle widening of the tines. It took 2-5 minutes for each --- and after they are just incredible pens.
I have a Black EF and it's a lovely, very fine writer. It's not QUITE as fine as my Falcon SEF but that may be a result of the work I did on the nib. Consequently though, it's a slightly wet writer which makes the EF nib feel even more smooth.
Then I have Yamabudo and Tsukiyo Custom Heritage 91s and they are beautiful colors for pens...
One of my favorite things about many of Pilot's pens is just how easy it is to remove the friction fit feed. (NOT the Falcon though, unfortunately, though my two Falcons didn't need any kind of adjustment.)
If you're using traditional inks and your nib is fine there's probably no reason to remove it, though. But like you say - it's NICE knowing you CAN if ever needed.
Edited by JunkyardSam, 27 July 2016 - 19:19.