Making a mod to do that is quite straight-forward. I've attached a zip file containing a demo mod - you can unzip to your My Games/Sid's Meier's Civilization 5/MODS if you want to test it.
Spoiler :![]()
Adding new terrain types however doesn't look as straight-forward. There must be an association between the rows in terraindef.csv and CIV5Terrains.xml but it's not obvious. Possibly it's in the SDK.
At least it is possible for someone to make a mod that recolours the base terrain.
How do you edit the registry?No you need to edit the registry as that thread says.
So here's our new tool, IndieStone Nexus Buddy. Based on the Material Maker tool it allows you to import an FBX and create a unit without even touching Nexus. Not only that...
http://www.theindiestone.com/lemmyandbinky.com/civ2/IndieStoneNexusBuddy.zip
You need to launch Nexus once before it appears