Hail fellow EB players!

I've recently begun modifying my EB game as to make it more fun for myself to play, as many of you others do. Now, I've got a couple of questions that I hope you, the community, can answer. Remember, I'm a complete newb when it comes to modding having only done simple things such as changing single scentences in one or two files.

What I'd like to know is:
- How do I alter unit recruitment? For example, I want Arche Seleukeia to be able to recruit Galatian Heavy Swordsmen in Thebais with a level 3 regional MIC. Wich files do I have to modify, and how?
- I've seen that MAA switches the colour and names of factions in the middle of his campaign to add flavour to his AAR's (Wich I'm a great fan of, by the way). How is this possible? How do you do it
- How do i change the skins on units? Or rather, swap. For example, I'd like the Makedonian Klerouchoi Phalangitai to swap skins with the Seleukid one. How do I change it?

I hope that my questions are not too cumbersome to answer, as I'd really like to modify EB for a even greater experience than it already is! Looking forward to hearing from you.