Your question is based on an assumption that Galaxy multiplayer service works in a way that is protocol compatible with whatever pre-existing multiplayer service exists in Unreal and that they could communicate with each other simply by changing the address of a computer in a config file. That is not how these things work however. Much in the same way one can't take an engine out of a Ford van and put it into a Honda car for example, or download your games from GOG.com using the Steam client. Two different technologies aimed to provide a similar end solution but which are fundamentally and mutually incompatible with each other.

In order for a game to be able to use GOG Galaxy multiplayer requires the game developer to purposefully enhance the game by modifying its source code to use the Galaxy APIs and link to GOG's libraries, then put out a patch to update the game and submit it to GOG for use in a future update. They can do this before bringing the game to GOG such as the case with Aliens vs. Predator 2000, or the new Double Dragon game, or they can do it by providing an update to an existing game if they decide that they'd like to spend the resources to develop that functionality and provide it as an enhancement to existing customers here. I don't believe any games in the GOG catalogue have yet received any patches from their respective developers to add Galaxy multiplayer support yet, however that will hopefully happen in due time as the entire Galaxy service offerings continue to grow towards official release.

Sadly, it's not a matter of editing a config file and modifying the name of a server though. If only things worked like that. :o)
In order to be able to do what you're asking for, GOG would have to have their own copy of the server side software which runs the multiplayer service of the game in question provided by either the game developer/publisher or by whatever other 3rd party owns the code. Alternatively a solution that is reverse engineered to be compatible with a pre-existing service would be an option and there are some of those out there also, although many such solutions are not necessarily on solid legal ground with respect to reverse engineering and intellectual property laws. PvPGN/bnetd for example is a open source 3rd party replacement for Blizzard's Battle.NET servers which can provide multiplayer services for most of Blizzards games including Warcraft III and older as well as some of the original Command & Conquer games. Blizzard sued the original authors of the code and won if memory serves correct even though the code lives on forever on the Internet and people use it. So in this case while some solutions may exist on the Internet for Joe Blow to download and set up on his own server with low legal risks as an individual for a given game, the legal risks to a company like GOG in taking such reverse engineered code and using it could potentially be great enough to land them in a lawsuit and is thus extremely unlikely to happen.

Short version: What you're asking for is impossible, and other potential alternatives people might come up with "because some program exists out there" are on shaky legal ground at best, which a company like GOG wouldn't touch with a 10 foot ethernet cable. That's why they're creating their own software, however game developers must update their games to use this service or else the given game will not be compatible and able to use it. The same would be true with Steam multiplayer service, or any other similar services that still exist out there as well.

Hope that helps understand Galaxy MP a bit more.

Update: One more thing... The likelihood of GOG updating one of the games in the catalogue to point to some other unofficial 3rd party provided game servers is extremely unlikely due to the same legal reasons, and would also require the publisher of the game to allow them to do so which is probably unlikely as there is zero quality control then over what some 3rd party service may or may not provide, whether it is secure/reliable/etc.

When the client has been sitting for a long time on the game library pages, hitting the page navigation controls or going to store view and back to library can cause the library to vanish and end up with an empty page. Only way to bring it back seems to be to close and restart the client.

Just installed Galaxy client after I received the invitation and having no trouble for this phase then I re-installing one of My games (Paper, Please) the client detect and recognized the game also get a small update (between 1 to 2 MB) and the update went smooth. now I can see my installed game under the "MY LIBRARY" tab while I clicked the game thumbnail or tab it doesn't showed up game detail, I assume it's because my internet connection (gog_gb_001).

Haven't try it for a multiplayer game (Alien vs Predator) but it doesn't bothered me much since i used gog for a single player games other Issue I encounter is a missing some games on my client library compared to the browser library. that's my quick report which probably a pretty common for a new tester like me i presume.

Other than around 60 games out of my 265+ not being seen by my client im having almost no issue with the client. Its clean looking, responsive. A tad primitive so far would like to see sorting by installed games and community integration (forums at least).

My one grip is download speed and an error i get when i try to install a game to a folder that already has a save file from a previous GoG install.

Have you tried clicking the "My Purchases" at the top of the screen? This seems to refresh the library view.

I just tried that now and it did indeed refresh and reload. Thanks for the temporary workaround until they fix the bug, beats restarting each time. :)

actually the oldunreal.com team had permission from Epic Games to make updated patches and add support for third party servers which are still up and running. I know a bunch of steam users are using the 227i patch to play online and get the latest bug fixes. I didn't know the online multiplayer functions were api based, just from knowing that I guess I should use the 227i patch and tunngle to play multiplayer games

Hello everyone. I have the alpha for a day and I have a newbie question.
In the settings menu section Download Path refers to where the installation files are downloaded?, can I indicate an external hard drive without problems? It is to save space on the main drive because it is a solid state drive. What do you think?
Sorry for my bad English.

That *should* work just fine. ;)

EDIT:

It will work but I actually don't believe it will work like your really wanting. In my experience the download path is just a temp folder for when the game is downloading, it then moves the folder to wherever your game library path is. So if you set your downloads path to your second hard-drive then your games will go there during the download but be moved to your library path as soon as it's done for installation, which means if it's set that as your SSD... you won't really be saving space other that *just* when your downloading that certain game.

Meaning you can't say download the game then install it later via a Galaxy direct download so you can remove / add games to your SSD to save space as you want. But you will be able to fully use standalone installers to get your games into Galaxy or backup the files in the future.

You may want to wait for others to chime in, but I believe I'm correct. xD

That should work just fine. The download will not take up space on your SSD until installation.

EDIT: Actually does the the marked place for downloads save the full installation though for a game? In my experience whenever I download a update or whatever, it's only available in the download path until it's done downloading it. It then moves the installation from the downloads folder to where you specify in The Game Library Path immediately.

Based on what he's asking I don't think it would do him any good other than just when the game is downloading, unless he also sets his library path as his second hard-drive and not his SSD because the game will be installed as soon as he downloads it.

Always glad to help.

Glad to see they are working on this client. I have just launched it and it looks good for an Alpha - only problem I have so far is it doesn't scale very well on high res monitors like 4k.

Yeah, doesn't scale well on 2560x1600 either. Lots of wasted whitespace and some of the fonts are so small you need an electron microscope to read. :) I'm sure that's temporary though. :) Hopefully they add elements of responsive design to the UI and content so that it works well on everything from low res mobile phones to 30+" high res displays.

Looks like this client has got some trouble listing all the games I own. I have 399+1(the Galaxy Client) games in my library, but the Galaxy Client Alpha only shows 322 products under my library.

A suggestion to the UI if I may? Add a "back" button that takes you back to the previous page you were browsing would be great, and the ability to use the dark background like on the site. And maybe ability to set the games to be listed as one long continuous page.

Also, tabbed library browsing by game category would be good, maybe even add custom categories to sort things by.

So far seems to run fine, even though I had to reinstall all my games (for now).