PATWEST=If you unpack the pak files it creates a new folder within the packs folder thats essentially inert. Any changes made to that file are irrelevant unless you first move the folders within to your main data folder and make a blank pak file. Then when the comp looks for a, unit card say, it looks first to the apropriate pak folder if it doesn't see what its looking there, it looks in the main data folder and see's, in this example, the UI folder there. It will crash if it doesn't see the packed UI folder, you have to make a blank pak file of the same name to fool it.
One last thing halie satanus, you can keep the unpacked folders there or store them somewhere else so later you can use things contained within. I've made use of the UI folder to change the unit cards for the mercenary's and to add building graphics to other cultures. Thats when you'll need to move the UI folder out into your main data folder and make a blank copy to sit in your packs folder. Otherwise it just defaults to the packed pak file instead, though thats not the entire story.
You can make these extra folders in your main data folder and leave the pak files alone if you're adding new items that are not already in your pak files. Because the mercenary's were well defined across many files it was quicker to change the unit cards even with all that crap than go around and rename them.