I don't think this is currently possible. I could be wrong though.

Steam recently gave me the power to remove games from my Steam Account.
I took greeat pleasure in deleting every Steam Game I own, that I subsequently bought on GOG.
I'm an Intensive Mod user and Steam is the absolute worst place to mod any game.

Uplay would be, but Uplay don't host moddable games and I don't buy any games that only use Uplay.
In fact All but one of my few Uplay games, came free with hardware, Zombi, I got on Steam, before I realised/
That's even worse, it needs Steam and Uplay. WTF!

GOG Galaxy is at least optional and sset for each game, but no online client is suitable for modding.
GOG provides Manual Game Installers, which are ideal for modding games.
So far I've Deleted these games from Steam

Metro - Last Light (Redux on GOG)
Metro 2033 (Redux on GOG)
Myst - Masterpiece Edition
Myst V - End of Ages - Limited Edition
Real Myst
Real Myst - Masterpiece Edition
S.T.A.L.K.E.R. Call of Pripyat
S.T.A.L.K.E.R. Clear Sky
S.T.A.L.K.E.R. Shadow of Chernobyl
Star Wars - Knights of the Old Republic
The Elder Scrolls III - Morrowind
The Witcher - Enhanced Edition - Director's Cut
The Witcher 2 - Assassins of Kings - Enhanced Edition
Uru - Complete Chronicles

The one exception, is completely different on Steam, it's mods are incompatible with non Steam versions.
Star Wars - Knights of the Old Republic II - The Sith Lords

My ambition is to delete all Steam games, the fact some are Steam exclusives, hinders that.
For the last year or 2, I've lost interest in anything released on Steam.
The only games I've boughtin the last year from Steam, I don't expect to see on GOG for years if ever.
Fallout 4 and XCOM 2 (No Pre-orders exemption - Seen Demo and want file access to start modding before release).

The so called 8-bit revival leaves me cold, Steam appears to have regressed in time and almost all Steam games appear 8-bit, I'm sure many aren't, but give me that impression, so might as well be.
I was gaming when 8-bit was cutting edge. I couldn't wait to dump it when 16-bit appeared, but few 16-bit appeared. 8-bit worked on both. Much like today with 32 on 64. Evbentually I drifted away then 15 years later. I saw Tomb Raider 4 offerred what I'd expected in 1985. It was 32-bit.
Now here I stand having bought my first PC (C64 then Amiga before 1985), a 64-bit PC in 2005, 10 years later, I don't consider 32-bit acceptable any more.

So Steam sucks, not eathshaking news, despite Valve fanboys denials.
Indeed I've just surprised myself.
10 years ago when Console exclusive deals got worse, i switched from only playing on consoles, to only playing on PC. Vowing never to buy another console, I never will.
I've just made a similar vow on the Steam forums.
I got XCOM2 early to access the files and mod it before release. That's my last Steam purchase, until the client is optional (that will never happen), I said Steam Exclusives, in reality if it's not exclusive to Steam I already don't buy from Steam.

So now I'll just keep whittling down that library until it's gone fior good.

Which brings me too wanting to remove some games from my GOG Library.
Specifically, Free games I never wanted in the first place. I have already hidden them yet get update notices anyway.
Speaking of update notices, I only use Windows 7, I don't want to see Linux and Mac updates.
I should be able too switch these notices off in my site settings.

So long story short, Steam rules GOG drools?

I guess you should contact support team.

Some of those free games are fucking great games.

On Steam if you ask VALVe's support to permanently remove your video game(s), later on if you want that video game back you can ask their support again and you get the video game(s) back and you don't have to repurchase it (them) again.

On gog.com for some reason you have to repurchase the video game(s) again. I don't know why, but it's stupid.

I still don't understand why anyone would want to have games permanently taken off of their account when they could just use the Hide key instead. But having the Hide key set to ignore any updates for the hidden games would make a lot of sense. Would that be possible on GOG?

I just seen the OP'S thread on steam has been locked.

Just think how it would be if the did censor unwanted posts.

^ This 100%. I hide the video games I never play anymore on my Steam account video games library.

So you can't actually permanently remove a video game on Steam then.

Although I still don't see why anyone would ever want to do this.

I guess it's because even if you hide them, your subconscious will tell you that they're still there. They're only gone when you know you can't access them any longer. I think it makes a lot of sense, buy a game on a disc (without a Steam/UPlay/Origin key), should you no longer want it throw it in the trash or break the disc. You won't be able to piece it back together or search wherever the truck unloaded it. Completely removing it from your library ain't much different.

And now people you know why support of all popular services is crap. If you have 10 like this every day, you'll need new people every week because the old ones will be interned in a mental hospital.

Everyone with Fallout wants to know how we can permanently keep games. :P

its like a fucking yo yo
i dont even pay attention to it anymore