Nope, I don't add any XML in my Test mod. I simply take the granary (for example) and change the 1 line of ART_DEFINES for the folder and nif.
I've heard such horror about the Civ4LSystem file that I've washed my hands of it.

For my buildings I don't need to mess with it. Kael said it was the 2nd hardest XML file to modify and that was enough warning for me.