[quote=Meeky]
Question: if I want the superior firearms export (I have the imports needed to make it now), do I add it to my list of exports or do I have to replace an export?
[/quote]

You add it to your exports. The only time an export is removed, is say in the case of Superior Conventional Weapons, that would replace Conventional Weapons rather than stack.

Edit: Oh, and warhorses. They'd replace normal horses.