1. Log into the account which has the high stats
2. Go to Zombie/Multiplayer headquarters
3. On your controller, click the middle button and switch to the account you wish to dupe stats too
4. A message will pop up, spam "B" and quickly switch back to the high level account
5. Go back to "Xbox Live"
6. Click the middle button on your controller and go to "Settings"
7. Once at settings click "Network Settings"
8. Click "Go Offline" and then click "Go Online / Online"
9. Open up WWII, you should have an error, click "A"
10. After clicking "A", press the Guide/back button (The 3-lined button)
11. Switch to high level account
12. Click again and switch to the account you wish to have the stats on
13. Turn on UDP Unicorn. I recommend the following settings,

Target: 27.27.27.27
Port: 3074 (Type that in or use Xbox LIVE default)
Packet Size: 1
Delay: 10
Threads: 9
Sockets per Thread: 20

14. Click "A" until you get into headquarters/zombies headquarters
15. Join a match, get a kill and your stats should stick


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Hope this helps some people, I know the others are confusing, don't know if this is any better. Let me know how it works!