Yes, this is possible.
There are some good reasons to do this. For example, if you're collecting data over time, you may want to keep the same version of the FOVE so all your data is collected with the same version of the ET algorithm for maximum consistency. However, you may want to be able to do development on the same machine using a new newer version of the software.
Of course, the simplest thing is simply two have the installer for two versions. You can simply uninstall one and reinstall the other at will to switch versions.
However, you can install both versions to separate directories, for example C:/Program Files/FOVE and C:/Program Files/FOVE_alt. A FOVE installation is just a series of exe files in a folder somewhere, and a Windows service pointing to FoveService.exe.
Since only one Windows service is running at the same time, when you want to swap, you need to swap which one is in use. You can see the currently used FoveService.exe from the Windows Services menu.
When switching versions, you need to uninstall the service, and reinstall it from the new location. FOVE provides two handle helper scripts for this in the installation directory. You can first run the UninstallService.bat (from any of your installations, doesn't matter which one). Then afterwards, run InstallService.bat from the installation directory that you want to use next.
Important: Both scripts must be run by right clicking and running as administrator.
Then you can confirm from the Services menu that the FoveService service is present and pointing to the right installation.
Note: These instructions are Windows specific. On Linux, the concepts are similar, but it's simplified since there is no service. Setup two installations anywhere on your disk, then run fove-service from whichever directory you like. fove-service automatically launches the compositor and such from it's own installation directory.