I've tried a number of different applications to open binary files. The one that I've used and enjoyed the most is called
bless and it is really easy to install. Simply open the terminal by pressing CTRL+ALT+T and type
sudo apt-get install bless and press ENTER. Note: You will have to enter your password, when you enter your password there will be no indicator on the screen, no asterisks, and the cursor will not move. This is normal behavior. After entering your password press ENTER again and follow any additional instructions given.
As a hex editor,
bless has lots of features and is actually surprisingly light. This should open your game file and allow you to edit it. I can't actually help with anything beyond that as I am not a gamer. However, it's in the repo and is easy enough to install without taking up much room or being overly complex.
You can read more and learn more about
bless by clicking here.