Here I'll explain in a few easy steps how to have multiple installs of any mod (with submod) at the same time. The first tutorial is if you have a vanilla (No submods installed) install of your mod. The second tutorial at the bottom is for if you already have a submod installed. In this tutorial I use Third Age Total War with some different submods as example.
I hope this is a useful tutorial. Please report spelling errors, etc. Also other feedback is appreciated.