Why: This would not only rise the game popularity but allso add a new community like moders
How far could you go wiht the mods: Only pictures and textures.
How the user would be ablo do activate a mod: Go under settings and there is a extra menu if you click on that a new menu will open up where you can choose mods. https://goo.gl/photos/C8UrCrQHtnxmZxJ89
Some exampels here: https://goo.gl/photos/PW6Kz1J9iafbv2q99
How would the mod work for game developer: The game looks if a mod is activated. If it dedects that a mod is activated. It does not ask icons from the server but looks for icons from a local folder (the folder name is the mod name!)
What happens if a icon or texture is missing: if a icon or a texture is missing from the folder it will ask the file from the server.
How the mod community works: Is that you make a folder that is placed in invasion game directory and that folder has all the needed pictures and textures.
What we need from Tap4Fun: One demo folder that has all the icons and textures. And that the software has a small line of code that checks first if any new location is selected where to ask for textures.

If any more info is needed i would be glad to answer!