1) Asset Bundles are one way, bundles created from the same project as the one they will be loaded into can have script applied.

2) Loading textures dynamically is another.

// Get the latest webcam shot from outside "Friday's" in Times Square
var url = "http://images.earthcam.com/ec_metros/ourcams/fridays.jpg";
function Start () {
     // Start a download of the given URL
    var www : WWW = new WWW (url);

    // Wait for download to complete
    yield www;

    // assign texture
    renderer.material.mainTexture = www.texture; 
}

3) Mesh can also be added dynamically from text by serializing mesh

4) Another might be to create a dynamic unity scene that only has a 'Code' node and then attach a script that loads in configs from local or web (i.e. in a JSON or XML file). Based on those configs you dynamically create all objects in script/code by downloading asset bundles or objects such as textures, meshes, configs.

Certain areas could be managed with any one of the above options individually or combined.

But the best option is to probably do assetBundles and using them from the same project when you export them to use script across them.

Simply, try to learn other programming language, such as VisualBasic (Visual Basic 2008 Studio), it is very simple and you can make your own updater. It can download files, unrar them to selected folders & etc... Very powerfull language, i have maked something like that (updater for my other program).

Or publish your game via Unity Web Player.

Occam's razor -- host in the web player and cachebust?