Hey!

Can you update the game through the offline downloader and do you have to download the whole game again or are there small update files?

Thanks in advance!

The offline installers get an update patch you can download.
However, whether that comes out at the same time as the galaxy version is up for some debate.
Threads https://www.gog.com/forum/general/disappointed_and_frustrated_with_the_lack_of_care_put_into_maintaining_offline_installer
https://www.gog.com/forum/general/gog_neglecting_offline_installers

Thank you very much! I get a 404 Error if I click on your link, could you please send it again? :/
Edit: The second link worked! Thank you very much for your help!

If you mean GOG Downloader (a separate program to be installed first), then it was discontinued a couple of months ago: https://www.gog.com/forum/general/we_say_goodbye_to_gog_downloader/page1

But you can just download from the website using your browser. I've never done pre-orders but for every game I have here on GOG, whenever there was an update, there was always a separate patch installer provided, so you don't have to download everything again.

Ohh, that sounds perfect! If I can always use the updater it is perfect!

Whoops!
Somehow the s got chopped off the first link!
https://www.gog.com/forum/general/disappointed_and_frustrated_with_the_lack_of_care_put_into_maintaining_offline_installers

It's a CDPR game, so one would think that the offline installer versions of the patches will be made available with the highest priority.
We'll see.

Thank you all!