Potential method for erasing your high scores post-NXE
 

Credit goes to Lightning 009 from TrueAchievements.com. Personally I couldn't get this to work because I would sign in too fast but I'm interested to find out if anyone else can get this to work...

First, you'll need a secondary profile. Setup your 360 to automatically start the game in the game disc (at startup) and automatically sign in to your secondary (boosting) profile. Now with Civil War disc in the tray, and both settings applied, turn off your 360. Now turn the 360 back on (probably with the controller because you'll need that ready to go in just a second). Here is the key, you'll need to press the guide button and be ready to sign in to your main profile before the secondary profile signs in, and just soon as the little indicator pops up showing that your secondary profile has signed in you'll want to sign in with your main profile. This should erase all of your mission progress and high scores.

As I stated before, my secondary profile was signing in before I could even get the guide menu open, but its worth a shot. Perhaps my internet was too fast? Be sure to post results if you make an attempt(s).

Well I have even went as far as messaging the guy on XBL, but i still can't get it to work. he said:

I asked if he had a video of how this worked for him, but that was the response.

I STILL cannot get these stats to erase or anything :(. any ideas? anyone have luck. I wouldn't mind getting rid of this game forever, but as long as this one achievement is still here, the game stays.

Yeah I'd love to get my last achievement, but I'm too lazy to keep replaying levels using mainly the pistol. For one thing I can't figure out how the scoring system works, and I'm pretty sure you need to beat your previous high score for the pistol kills to count.

I got it to work nice find.

That...
Is....
Not.....
Fair.......

i can't imagine how I can't get it to work at all for me. did you get a video of it or anything??

It did take me a few times but i did get it to work. Sorry i dont have a video camera and i dont have the game anymore. Just keep trying and you will get it to work. And i used two xbox live account, I did because the accounts have to connect to xbox live,and it gives you time to press the guide button and sign in.

Awesome awesome awesome!!!! Thanks for the tip

So let me get this right. Sign in "Boosting profile" then as soon as you see the sign in notification you sign your main profile in on the 2nd controller?

Yes that is right.

I think I understand how to do this, but I cannot get my xbox to auto-load the game, it always goes to dashboard!!!

Any tips?

I'm a few years behind the ball, but I'm definitely going to have to give this a try.