*Source code*, not data files. For instance, there's a MAX_BASES constant that's set to 8. You'd have to change the source and recompile.
And you'd also have to make sure that the UI matched. On screens with a 4x2 base-selection widget, for instance, you'd probably want to add scrollbars or pagination or the like if the code didn't automatically do that for you.
And I'm not sure why you'd bother (with the bases, anyway), because it seems unlikely that you could actually afford to have more than eight unless you have so few buildings and employees in them that you could actually make do with eight.
