Applications - Adobe - Flash Player

Adobe - Archived Flash Player versions
Adobe - Adobe Flash Player Distribution

Adobe - Adobe Flash Player Administration Guide

Adobe Flash Player as msi-file has some tips for installation of the MSI version in a company setting.

Installing an old version blocked after removing newer version

After removing a newer version of Flash Player an older version can't be installed because the setup of the older version blocks you from doing so.

The workaround is to delete the SafeVersions key in the registry.

On 32-bit systems: HKEY_LOCAL_MACHINE\SOFTWARE\Macromedia\FlashPlayer\SafeVersions
On 64-bit systems: HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Macromedia\FlashPlayer\SafeVersions