So I just downloaded the game on GOG. After that I noticed the free DLC in the store so I bought that too to maybe install later when I have more disk space to share. But now Galaxy is constantly trying to install it. I already tried disabling the DLC in the 'Manage installation' menu. But as soon as I close the game it tries to download again. Does anyone have any suggestions?

I have sort of the same problem, but maybe worse. I downloaded the offline installers for both Fallout 4 and the high resolution texture pack, installed the game, installed the texture pack, and now Galaxy has detected Fallout 4 and is insisting on installing all 58 GB of DLC... that is already both downloaded, and installed.

Hopefully GOG pushes a patch for this quickly, this is a real mess.

Same issue I have too. I have disabled auto-updating, even hide Fallout 4 in Galaxy. HD DLC is also unchecked in "configure" option under DLC page. Nothing works.
I have even scheduled auto-updating between 12:00 PM - 04:00 AM and it still tries update outside this time period.
Pause download still works, but must be clicked every time the Galaxy is started.
I play without Gog Galaxy running. Seems to do the trick. ^^ Don't need achievements.

For those who still haven't solved it, I solved it by clicking on the game options, go to manage installation and then configure. There click on dlc and uncheck Fallout 4 High Resolution texture pack.

I have Galaxy updated and auto updates for games disabled, when I configure Fallout 4 it says auto updates are disabled, and under DLC the hi res pack is unchecked, but Galaxy starts downloading it every time that I restart it.

Yes, rename the file. Change the extension to .old. Or whatever.

And why use it. The High resolution pack, bloats your ram. And there are better HQ mods on the Nexus.

I contacted support and am waiting for an answer. I can't deselect the DLC under Manage Installation, obviously a bug. Very annoying, would have bought the game from Steam if I had known about this issue before.

STILL not fixed?! Not a good show, GOG. (Not that anyone from GOG is likely to read this.)

Because this is the first hit on Google to this Subjekt, In short why you can´t install this in German.
There are simply no Files for the Texturepack in German on GoG. Obviosly Galaxy cant handle this and mumbles somthing like Connection issues.
Installing the English Version with Texture Pack worked fine for me.
Can´t understand why Galaxy can´t post a usefull Error Report on this.