For Steam: 1. Right click on KSP on list 2. Properties 3. Betas tab 4. Select "beta" of older version 5. Wait for download to finish 6. Local Files tab 7. Browse local files 8. Rename "Kerbal Space Program" to, for example, "Kerbal Space Program122" 9. Create shortcut because renamed directory is detached from Steam (no upgrades, no launcher) 10. Or add to "Non steam-game" to Steam launcher
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