The mods you can do is dependent on how much money you have, how mechnically inclined you are, along with resources available to you, and how much time you are willing to invest. There are not too many bolt-on performnace parts for an Express.
No direct replacement pipes, so you'd have to hack & weld something. You can't just pt a Dell or Mikki on it because there are o factory type manifolds available. Oil injection, choke, throttle cable are other considerations and complications.
If you are not going to build it up for performance parts (custom pipe, kit and intake) just make what you have work the way it was designed. They're a fun bike in stock form.
I have 2 of them. One performance Urban Express and also I ride an '82 Express stocker all the time.