O.o wow there are quite a few sites for this game... definitely found 7zip to be working the most consistently with no issues. Have compiled most of my files into merged categories. Gone from a few hundred to about 20. Thanks so much for the guides everyone! Soon I'll actually get round to playing the game...
The terrain merge is part of the ZT .exe program and it is illegal to change that. I have played with terrains myself changing sand colour and water colours. But to do that you have to overwrite one of the ingame terrains.
Here is a link to my attempts at this with Jay who is a programmer.
If you read further back in that topic it does say I tried with the swamp terrain.
What type of modding are you interested in doing?
You can always check out our tutorials here.
Also check out the designing tools here.
There are also several of us designers that hang out here. So if you have any specific questions that you can't find in those links, just ask and we'll do what we can to help :D