Maybe this should go in the mod forum, but since FoC is new, I might as well put it here--especially since I'm not offering anything to download.
First, extract the XML directory from Config.meg as normal. Then go to starbases.xml and open it up with notepad. Use ctrl+F and search for 'Executor' (without the quotes). You'll find a line that says "Uncomment this line to use Executor in multiplayer."
Well, do just that, and you'll be able to use the ship in skirmish mode.
Now, I'm new to modding, so how do I extract the XML files?