Steam's "Beta -> Previous Stable Release" will, in fact, roll back your game. However, it will send you back to 0.90(build 705), NOT 1.0.2 What mikegarrison says regarding copying the game folder is true. I have 1.0.4 and (now) 0.90 on an external drive. None of my mods work on it now, but the game runs. Just don't run "Launcher.exe" else it'll try to auto-update again (I'm told). Just run KSP.exe