Omg, it's more in-game content! How annoying!
Make a feature request in the GOG Galaxy forum if you want this function added to the GOG library.
It is annoying. I dont want to play the game in cheat mode. I shouldnt have to know that some items are not meant to be there and that you should avoid them if you want a balanced game.
I dont want to have to figure out why I am so overpowered in early levels and then realise after researching it that Bethesada tried to reward people who preordered with lame cheat items.
Loads of games have these lame DLC items. They are never good and never make sense in the game. They always make the game worse. The game is designed to be played without them. I never want them installed. There should be an option to uninstall any DLC that you dont like.
I honestly assumed there was such an option and that someone would point out what I missed. I am surprised that there isnt. Im really surprised people see mandatory cheat modes as more in game content.
Because it IS more in-game content? If you don't want it, don't use it. It's that simple.
Loads of games do have OP DLC items. There's a legendary sword in Assassin's Creed Odyssey iirc that makes any other swords you acquire pointless for a warrior build. I stored it on the Adrestia & never used it. Deus Ex Human Revolution Director's Cut gives you all the pre-order bonuses once you've completed the tutorial mission in the factory; one is a super OP shotgun. Saints Row 3 & 4 give you all the pre-order costumes & skins after finishing the tutorial levels, and I have to sit there like an idiot clicking "Accept" over and over again until the queue is cleared.
My point is that I get what you're saying. But I'd MUCH rather have the content than not. Do I want to dress up like a panda in Saints Row 4? No. But if wanted to, it's there, in my wardrobe, not bothering anybody.
Like I said, make a feature request to have this added to the functions & features of the GOG library & and Galaxy client. Until that happens, maybe you should play on Steam - which does allow you to disable the installation of the DLC for Dishonored.