For example, could I inject the Twilight Princess EU save found on this thread https://gbatemp.net/threads/wii-u-save-files-compilation.427761/ to my USA version of Twilight Princess?
I highly doubt it. However if you don't want to take a bad risk then make a backup of your current save file, inject the EU one, and if the game just hangs on the splash then it didn't work.
IF it doesn't work then delete the save in the System Settings.
