At 7th level, a Mechanic gets Expert Rig, which states:
Your custom rig has improved. Whenever you use your custom rig to successfully hack into a computer, you can also disable one countermeasure installed in the system (except firewalls). In addition, your custom rig can now be used as any engineering or hacking specialty kit of item level 6th or lower, and it has the features of a computer with a tier equal to half your level with the Artificial personality, hardened, or security I upgrade module. It also has an audio/video recorder. You can add extra modules or countermeasures to your custom rig at the normal prices.
So, 1) I assume that you can't add Upgrades (better security, etc.). Please correct me if I'm wrong. The reason I'm not sure is because the same paragraph refers to the "security I upgrade module". Actually, re-reading the section in computers now I'm really unsure....
2) What about the modules and countermeasures that are based on the base price of the computer? It's easy when it's installed, but what about when you gain levels? Does the module/countermeasure stop working until you pay the difference?
Thanks!