I'm used to manually installing all my GOG games and I like it that way. I tried Galaxy and I'm not very fond of it, but now I've got one game that I want to play in multiplayer with a friend and for that Galaxy might be be required or at least useful. Only, I don't really like having Galaxy checking on my manually installed games - I'd like to stay in full control over their state.

So, is there any way to use Galaxy only for speficic games and prevent it from touching any of the games I've installed manually, without the client? Maybe disable auto-updates, at least? Or can I remove GOG games from the Galaxy library without uninstalling them, just so they fall off its radar?

Install the client into a different folder than your GOG games just to be sure, but it doesn't go out of its way to auto-add already installed games. You can do it manually, but it won't detect them automatically.

I installed Galaxy into a flash drive then hid the flash drive under a dresser of a strangers house two streets over.
Successful partition
I'm not a fan of beta testing.

If you install galaxy, it will not search and recognize games that you install manually, unless you research them from Galaxy using the "scan and import folder" option in the top Galaxy Menu. In other words, you can install Galaxy, install the game you want from it, even add a specific game on your HDD by targeting its install folder while not "connecting" other GOG games you have on your computer.

As other said, you can also order Galaxy not to update games if this your choice.

I did that (at least this time, after uninstalling) but it still found a few GOG games and tried to update them. Ah, so you have to do it for each game individually? That's convenient and inconvenient at the same time .. But in any case something to go on, thanks!

EDIT: I've found those options, but they are greyed out and I can't click on Manual Updates for some reason ... Then I guess those added games are still remnants from the last time I tried Galaxy, before uninstalling it. Maybe I ran that scan and import function once, back then. Is there any way to undo it and remove those games again, clear Galaxy's memory of them?

It only allows it for installed titles I believe.

regarding the greyed out part - well that's weird - i can set the setting for all games manually (just checked for TW3, Jagged Alliance 2 and Sim City 2000 to be sure it works for old and new games. I'm using the GOG Galaxy 1.1.11 beta yes

Apparantly it was greyed out because Galaxy was already trying to update. I had to pause and abort each download individually and then I could set the update settings to manual individually as well.

I think I can live with the way it is now. Galaxy updates seem useful, but I want to be able to check the updates before downloading and installing them and to choose the right time for that.

glad you found a working solution for you needs!