So I took a look into modding Bronze Age (specifically, adding a new map), but I quickly saw that I would need some more xml details to make any progress. Therefore, when you get the chance, I recommend writing up a mapmaking guide. But if you have more important things to work on, I fully understand.
EDIT: I should add that I'm trying to minimize error reporting so you don't get flooded with messages about buggy mods; if it helps, I have a map (minicradle -- basically cradle of civilization resized to 50x50) that works for some seeds but not others.