Ok, heres something, EVERYTHING is replaceable and can be swapped out for aftermarket parts, well maybe not the banjo that goes from the reg, but everything can be swapped out for example:
Board - The internal valve that controls the firing etc.
Barrel - Barrel.
Bolt - The moving part that fires the pain down the barrel
Body - The outer coating plastic shell
Trigger - not much to say here
Bottomline - The stock ASA on the ion sucks, get and OOPS, or whatever your prefer
Grips - Grips
Regulator - Controls air flow into the gun
Feedneck - Holds the loader
Frame - Holds all the parts together basically the big black thing the metal part lol
Im sure others can name a few things... ive probably missed the obvious ones
OOPS stands for an On/Off Purge System - Its a replacement part for where you screw the air tank into and allows you to turn the air on/off. Because it has a purge it means you can not only turn the air supply off but also release any leftover gas in the ASA, so making the unscrewing of the tank so much easier (as there is no pressure).