running multiple _alt versions

[Volcano Man]

I am compelled to say: David Freer made the _Alt for K44, but yes, it is officially supported on my website (I don't want to take much of the credit). To answer the question though, you should be able to continue playing v3 and also v4 if you install the latest (although David would know better). What I mean is, if you started v3 already, then the scenario data is in your saved game file (either .bte or .btl). The only way this would not work is if some serious changes to the OOB were made, such as deleting units. I am unaware of that having occurred between those two versions.

As Rick says, you can back up the game by just copying the directory and renaming it to something else. You can either keep both duplicate game folders and run them separately as you want, or update the _Alt to v4 and see if both games run without an error then, if so, delete your backup / duplicate game folder.