
The game should save in the background as always.
Check your heroes once you're able, they should be rid of those dreaded quirks and diseases, even locked ones. There may be a black screen and some error messages nagging you about missing quirks that can't be added, but don't fright - because it worked for me. It should take a while for the game to adjust to your changes. Save your changes, start the game, and load. Leaving no empty lines between the previous and next blocks. Delete those lines and everything in between. Note the curly brace in the first line, and the brace and comma in the last line.
Delete the entire block the quirk is in. Open the original "quirk_library.json" with Notepad++ and search for an offending quirk. Go to your game's installation folder > shared > quirk > and backup "quirk_library.json". Note down which quirks or diseases you'd like to remove from your heroes and backup your. It specifically can only edit, add, or remove quirks. The app does not have that kind of power in your case. Some food for thought no one asked for: Buffs and Traits and their availability between heroes/mobs/bosses/trinkets can be edited. One I hope for is additional content I quoted at #1 and others are unlocked after completing campain mode or certain difficulties. I also think Darkest 1.0+ can hold many possibilities. That may require the devs to do a bit of behavior coding too. An exception is the absence of a "rule_type" that checks party members' class or relative rank (iirc checking the buff library). I think examples are also interesting and maybe do-able.
I am currently adding this feature plus others to the app for the sake of being thorough. I also made a few test quirks that cause the hero to say completely NEW dialog when, for example, interacting with curios, and negative ones that can completely trash a hero. The one I'm showing was just an OP example. I agree that the game doesn't need more quirks in general, but rather "unique" ones.