When you are unable to see the change when you download new maps to the game, are you putting the files in the correct folders? For the most parts, all of the map files you receive should be placed in the "exports" folder, which can be found in the C:/>>FeralHeart>>exports folder, unless the maker or ReadMe file says otherwise. As for the markings, these files also need to go in specific folders. Most of the downloads that you install should contain some sort of ReadMe or Read This note inside of the download that explains where the files go. The reason you are most likely seeing white, textureless "marshmallows" is because you haven't downloaded markings that other users are using- in most cases, downloading Mass Markings can help fix those marshmallows right up. c:
If you're having issues installing maps, markings, or any other files that you download into the game, some popular programs are WinZip and WinRAR. They're very handy for unzipping files.
Also, when you've downloaded the markings/maps, etc, be sure that you completely close out and re-start the game.