Grimrock

I don't have a save before entering the prison, the last auto save is old (level 6) because I was hunting missing armour parts and areas throughout the whole dungeon. Is there a way to edit the current quick save so I can leave the prison? Or mod the game itself somehow to achieve the same? I have tried Glyn's save editor but I guess it doesn't work any more (says my saves are all invalid.)

By entering the prison you started the final phase of the game. Without hacking your savegame or using the console there is no regular way to get back to the upper floors.

Then: which achievements do you want to complete anyway?
Very few are tied to dungeon levels i.e. "Seeker of Secrets" and some of these even require that you enter the prison.

I've activated the console now. Does this deactivate achievements?

To-do:
- Seeker of Secrets (got 67 of 71)
- Treasure Hunter (got 6 from 7)
- Skull Snatcher (got 4 from 5)

Got past the door using this command:
party:setPosition(22,22,0,12)

I'm not sure exactly how Achievements are coded, so I can't say if simply activating the console would somehow block them, but I seriously doubt it.