Need help changing existing civ icons

I'm currently working on changing the colors of all the in-game civs to be more natural colors which are easier on the eye (ahem, Morocco). Rather than make a mod, I'm changing values directly in the xml so that I'll be able to play with achievements and in multiplayer. So far I've figured out how to change the colors in the xml files to get icons and cities the right colors. I've also located the dds files which contain the symbols and their colors, and begun editing them in photoshop.

The problem is I'm not sure what to do with them now. I can't reinsert them into the pkg file they came from, but I don't know where to put them and which references in other parts of the code I would need to change, if any, to get them working correctly.

If anyone can offer advice to help me figure this out, I'd greatly appreciate it. Hopefully I posted this in the right spot too - I didn't see anywhere for help requests.

Drop your replacement .dds files into the assets folder (it doesn't matter where) then set LooseFilesOverridePak = 1 in the config.ini.

(And, yes, this is the right place.)