may need to set permissions on file
You may need to set permissions on the file before you can save. Using "File Manager HD" I had to enable root explorer and mount systems folders under the settings and then add write permissions to Group and Others in the permissions dialog, probably don't need Others but I am lazy. Don't forget to change the permissions back after you save your changes. Incorrect permissions settings can sometimes really bork things.
Also seems that the settings might be a little different under ICS, I am getting "Touchscreen Toggled" instead of the menu after setting 150 to MENU.