- Let Steam update DayZ without opting into Experimental.
- Copy the folder "DayZ" in ...Steam/Steamapps/common to some other location.
- Start Steam, right-click on DayZ, select Properties, Betas, opt in to Experimental.
- Steam will then download the necessary files for Experimental version, overwriting the Stable install.
- To switch back, you normally would have to opt out and let Steam then reacquire around 5 GB.
- To prevent that, a popular workaround suggested just using such a manual backup of the game folder (Steam/Steamapps/common/DayZ).
- This is no longer working, Steam now re-downloads the entire game regardless of such a manual restoring operation. While I can't rule out the possibility that it's only me and my machine somehow, at least here it was reproducible.