Hoschilein... Macht das nicht das hier schon?
https://community.bistudio.com/wiki/Game_Updater
Zitat:
This application aims to improve the experience of switching between Steam branches of the game by avoiding the inconvenience of additional downloads every time you change. It downloads, install and update additional copies of Arma 3 from different branches (Main, Development, Legacy and Release Candidate).
Xeno