Bit late with a reply, but well, it's one of the unused features of the editor, just like there are reference's to 'castles' and other unused stuff. It's not for this game those features.

You'd need a whole lot of assets, very specific files and scripts to get this feature to work and then it still wouldn't be ingame to be playable yet.

Tile cover specifically would put deco on texture tiles if remember correct, like pebbles on the ground or grass on textures (actual models, which aren't ingame).