It's better to include in the OP that unzipping the compressed file to /terrain will overwrite the original files, so if people want to revert the changes they need make a backup copy of the /terrain folder. Changing the original files will also affect any mods that depend on those files.
You can avoid all this if you simply make a separate mod containing the changed terrain files, using a ruleset to change which terrain files are used on the vanilla terrains. That way players can simply switch the mod on/off in Options without having to copy/replace the original terrain files
