I'm not sure where or when I originally posted it. From the dates, it seems that it was in the beginning of 2005. I found the zip I probably posted, so I'll attach it here.
It's not a simple process, and the guide isn't that good either, but it should get the job done.
Hm, would it be possible to mod in different map-screen temple graphics for different empires? I always thought it would be cool if Mictlan's temples looked more like they actually do.