So after many days of growing more gray hairs...
I finally found out what was wrong with all my game save's Keys showing up as "UNREADABLE"
When I installed Bruteforce Save Data into it's default path:
C:\Program Files (x86)\Bruteforce Save Data
...the permissions of that path were very strict, not allowing me to edit games.conf, etc..
So I wiped the installation, installed it without running it as Administrator and just installed
it into it's own folder inside of the Downloads folder:
C:\Users\User\Downloads\Bruteforce Save Data App
...entered my profile info/global info and it worked like a charm.
I did a test on a new game of The Last of Us (physical disc version) and I successfully applied cheats.
I added the titleID (NPUA81175) of The Last of Us: Left Behind Standalone and made a copy of the main game's save patch (BCUS98174.ps3savepatch) and changed the titleID on it too (NPUA81175.ps3savepatch), so that the same cheats options would show up in the selections.
I applied cheats, encrypted it. loaded it on the USB flash drive
-Transferred to my Playstation Plus online storage
-Launched the Playstation store
-Navigated to the Playstation Now section
-Launched The Last of Us: Left Behind
-Opened Playstation Now XMB
-Copied the modified gamesave from Playstation Plus online storage
-Resumed letting the game load...
-Loading...Loading...error! : ) it said the save was corrupted.
Some interesting details... when you look at the The Last of Us: Left Behind save data in Bruteforce Save Data pulled from the PS Now cloud account, both the profile and the game save have different PSIDs, but the same np_account.
I tried re-assigning the PS Now gamesave to match my actual PS3 console's data/profile, re-uploaded it, and still, the data was corrupt.
I have no idea how to approach this given that the gamesave/profile from the PS Now cloud account has TWO different PSIDs, and my console's PSID is different from both of them too. Anyway, thought I would share an update. Any ideas?