It's been bothering me for a while, as I am yet to find a way to do this.

To clarify things: say I want to play Arx Fatalis.

1. Game location Galaxy\Games\Arx Fatalis;
2. I then install Arx Libertatis in Galaxy\Games\Arx Libertatis;
3. How to make it so that when I press Play button in Galaxy Client, it would launch Arx.exe from Libertatis folder instead of Arx folder?

I'm mostly interesed in this to keep track of playing time as well as not having to open different folders all the time.
I changed paths of executable files, etc, copied new exe file to original folder and then altered the path, etc. Nothing seem to work.

Please advise.
Thanks you.

I am unsure if there is some way to make it work, but to me it appears you are basically asking "How can I run a non-GOG game with Galaxy", and currently that is not possible AFAIK, like it is possible with e.g. Steam.

At least when I googled for that Arx Libertatis mod, it seems it is like an open source "remake" of Arx Fatalis which just uses some assets from the original Arx Fatalis game, and also the point that you are supposed to run a different executable from a different directory.

Anyway, thanks for letting me know of that mod. I've been meaning to play Arx Fatalis, and I need to check if playing it with that mod would make more sense, or should I go with the vanilla game at least at first. Does it fix severe bugs etc.?

Thank you, Thiev, for your time.

I'm not entirely sure I understand what you mean. I looked in both game folders (Arx Fatalis & Arx Libertatis) and Galaxy folder, but I couldn't find the .info file you mention.

Am I missing something?

Looks like this feature is now implemented in the client. Click the 3-dot menu, go to manage installation/configure/features, add a new executable and mark it as default.