Did you make many mines or buildings in your savefile, @giladthebut?
Does the game crash to desktop, or is it that you get an engine error and the game becomes laggy?
To remove the shortcut from the x, try adding your own keybinding (see Help needed for use user_bindings (Key binding) for how to do it).
At the moment we can’t remove a shortcut, we can only assign it to another key, and if that key is assigned to something else, it will activate both things, but that will change soon (not sure when we will get the UI for keybinding, though).
If the crash with the x-ray mode is only happening on that savefile, could you upload it? We can take a look and see if it crashes / lags also for us.