[quote=@Duthguy]
The metal mind perk provides an extra mod for the framework but what exactly qualifies as a mod? Does it simply mean an extra primary or secondary system or something else?
[/quote]

It means a custom modification for the Framewerk: not something as large as an entire Secondary System, but it can be a new feature or addition. For example, a mod could include a change to the ammunition of the weaponry or the firing method to them, or for the torso to be able to turn 180 degrees from the legs. Given enough time, a Metal Mind can customize their Framewerk pretty considerably compared to other pilots who can do smaller changes.