..open up the save file in Notepad and ctrl+f through the code to find the right section. Search for something recognizable like tinderboxes and click find until you reach something familiar, then I typed "health" from that spot and it took me to the right code. It will looking something like "99999.999". I went in and changed it to "30.99999" or something similar. Then save the code and start the game. Check your health and it should be right and you are nearly dead. Should only take a few hits from the monsters to get to the prison cell area. Then starts cheats again.
While this is part of the April 1st "potato" joke the Steam version was updated and I guess a retail patch will follow shortly.
Not just a humor update though as from browsing the files a lot of other stuff was improved such as proper support for new GPU's like the 500 series and ATI 6000 series, shader and localization fixes and certain balance and gameplay tweaks.
Haven't found a changelog but the exe did change so a trainer update would be welcome if the title is still supported.
Unfortunately I did not find a changelog yet but I'll keep looking for more concrete info, this is the link to Steam's news section of their website and as seen quite a few other titles (And some unlisted ones like The Ball getting a UDK update in the progress along with that potato joke.) were also updated, overall it's sort of a joke update but many other unlisted fixes and improvements were added in to these games.
(Just trying to be helpful by pointing out when titles got updated if it hasn't been mentioned already, this isn't a direct request for a trainer update but more of a question if one is planned, would be nice with continued support but this particular update pack covers a lot of titles though I only own Ball and Amnesia myself so I can't comment on what the other titles got updated with in addition to this potato themed joke.)
Game crashed on me with the trainer active when I hit the Esc key. Getting this error; "Amnesia.exe caused an EXCEPTION_ACCESS_VIOLATION in module Amnesia.exe at 0023:004660F3" Using the Steam trainer (the latest listed). A fix would be wonderful.