I can only work in hex, so that is a massive, task. Generally it is a matter of looking for something that you expect will be there and figuring out how it is handled in the unreadable portions!
Edit: I just had another play with it, and basically the list of valid civs seems to be definitely hard-coded at address 0x5FF614 of the .EXE. I tried to insert another entry in this list and the resultant .exe crashed.
My attempts to add a new Major God using the MajorGods.xml and changing the uigodpicker reoutine was unaffective - I would get its icon on the screen, but selecting it had no effect. My guess is the select which would need to establish the link to an Age 1 tech fails, because it isn't in the list!!
So unless someone can figure out how to add to this list, I cannot see any other way to deal with it, other than the earlier suggestion of Making Age 1, a culture choice (greek, romas, sumerian, etc), and the first age up where you select the civ (major god).
[This message has been edited by Stephen Caines (edited 08-04-2008 @ 09:49 PM).]