waltc: Thank you very much..! This is the sort of thing I was hoping to learn...I see that I simply didn't look hard enough. Thanks again...!
And thanks to everyone who replied...;)
There is still gotcha with the force-import feature. I tried that process on maybe 50 games I had installed pre-galaxy. If Galaxy can recognize the game with top-left + button, there is a good chance that it won't have to download anything additional. Or, it will say that "the version you are currently on is no longer available" in the game details, but will let you keep it that way (you have to go to configuration and enable manual updates to see it, I guess that if you don't Galaxy will eventually decide to update it automatically, but I never let it get that far).
Using the other way to import, there is good chance that it will decide to download the whole game. And there is no way to uncheck automatic updates until the download completes and you get to the configuration screen. If you need to worry about your data cap, you should watch the import process, and when "downloading 20/20GB" appears, you have the option to cancel it. It seem Galaxy won't touch your game folder until the download completes, so it should be safe.
Just tried it on some oldies to be sure it wasn't fixed yet. Divinity 2 - wasn't recognized, importing folder did work and didn't seem to download anything. Both Kings Bounty Legend and Crossworlds were not recognized, and downloaded the whole game when force-imported from library. I made backup of Crossworlds before doing the import, and only thing different are new __redist and _lang folders, about 400MB - nowhere near the 5.7GB downloaded.