Dear GoG, I think you should improve the way games update in Galaxy.
Having to download a game again because of a hotfix that weighs only 43mb is... let's say, not very convenient.

Agreed. I had to spend the entire day downloading a patch bigger than the install files.

Yap, that's ridiculous.
I guess this has something to do with Unity. But it should be possible to generate a binary diff and patch only the changed stuff.

Edit:
There is a free Lib at Unity's asset store...
https://www.assetstore.unity3d.com/en/#!/content/18438

If somebody reads this from in inXile, just give it a shot. You would help a lot of users, because not everyone has a 50+ MBit connection.

Next time when you will install "offline" patch and for some reason you want to run a game through GOG Galaxy do this:
1) game patched but Galaxy is trying to download "huge patch" again?
2) move entire game's folder to other place (on the same drive to make it quick),
3) wait until Galaxy will lost trace of a game,
4) move it to the old place,
5) "Search and Import" folder in Galaxy,
6) watch how it's "updated" in GB/s speed,
7) play...

It worked for Witcher 3 so it should work for other games. Yes, I hope too they'll fix GOG Galaxy client soon.

Nothing to do with unity or stuff. Just a weird galaxy choice.

I don't use galaxy (why would anyone ever ever want to, anywhere ever why just why seriously why), and so I just downloaded a quick 40 Mb patch from the gog website (using the gog downloader, but a direct download was possible too).

I even first thought that the OP had done something wrong (apart from using galaxy), but apparently all those who used galaxy have faced this behemotic re-download issue. So.

HEY, YOU READER - IF IT IS NOT TOO LATE FOR THAT : just download the tiny patch separately from the gog site, instead of trying to do it through galaxy.

Because this is a thing.

Gotcha. There is no separate Mac Patch :/
I haven't known that you can download separate patches in general from the Shelf. So thanks for your advice :)

Yea, I just installed the 43 mb hotfix patch off GOG. I don`t use any of those fancy d\lers- No need for it. And all is done! :)

Which is why I uninstalled Galaxy. The resume feature is rather wonky. The old download method works better IMO.