This is for Windows. Not yet tried on different OS.
Tip: Play the game first up to the trapdoor scene before doing this.
1. Go to My Computer > Organize > Folder and Search options > View Tab > Select Show hidden files (skip this if hidden files are already visible in your PC)
2. Then proceed to this directory > C:\Users\Ella\AppData\Roaming\Big Fish Games\Mystery Case Files 13th Skull CE
3. Right-click the file with this file name > [your username].profile, open with Wordpad or Notepad++ (if you have).
4. Find the code that says,
change the 5 zeros between the <int> to 1,2,3,4,5.
5. Now, search for OpenTrapDoor, change true to false and save.
6. Go back to the game, you can see the the goblets are completed and the trapdoor is open. Get the half gold medallion in the goblet cabinet.
7. You're done!