This tutorial shows the various techniques I have used in my own modding. They are not the only ones and are not necessarily the most efficient ones, but they should work for you as they do for me.

Desiring to replace the L4D2 survivors with new people from time to time, I looked for addons to do so. After enjoying several survivor addons, I wondered what it would take to create my own. Eventually, I found a tutorial by da1barker, Custom L4D2 Character Step By Step or Custom L4D2 Character (same tutorial, different websites), that explained everything in enough detail for me to try modding my own survivor replacement. After converting my first survivor model, I wanted to share what I had learned (which also helped me from forgetting how to do this modding).

The tutorial by da1barker explained how to use 3ds Max for the modeling, but 3ds Max was not available to me at an affordable price. So, I originally used Autodesk Softimage Mod Tool for the modeling because it was a free program (and might still be). Mod Tool had several problems specific to modding L4D2 survivors, so I eventually looked for a different modeling tool. I now use Blender, because both the main program and its plugins are open-source, free from any fees, and updated frequently; thus, when problems arise, people can potentially fix or workaround them.

NOTE: To keep it simple, the instructions give example paths, folders, and file names. For some computers, wherever "C:\Program Files" is used, you might need to use "C:\Program Files (x86)".