VIDEO: Freth's video on how to run an alt with Wurm Unlimited

1. Go to your WurmServerLauncher folder.
2. Copy the file named steam_appid.txt to your WurmLauncher folder.
   

Read the paragraph below.

You can now run more than one copy of Wurm, but you must run subsequent copies of the launcher from outside of Steam. The best way I've found is to right click on the already running Wurm Client icon on the taskbar and run another instance of Wurm Client. I keep my Wurm Client pinned to my taskbar, so that it is always there and just load it from that icon for both the primary and alt instances.