Is there any way to fail Delvin's "special item" quests?

Anytime I find something cool, I get a quest to bring the item to Delvin.

I want to put the cool items I find on display in my house, but since they're quest items I can't remove them.

Any way to purposely fail these quests? Would using commands or a mod to kill Delvin work?

Solution 1:

If you just want the items as you say then you can get them. They will eventually appear inside of the thieves guild on the shelves and desk and such by the guildmaster's desk as seen on this picture from the Wiki

To avoid spoilers I will just post a link to the Wiki here and you can go check out the names of all of these and how to get them if you like.. But the overall point is, they are not whisked out of existence, they just take a bit of time to show up again. Just like the Golden Claw in Riverwood you can pick them back up after finishing the quest.