I see that you have comments on both answers that talk about applying changes to all CKEditor instances. The following code should allow you to override settings for all instances
window.onload = function(){ CKEDITOR.on('instanceReady', function (ev) { ev.editor.setKeystroke(CKEDITOR.ALT + 48 , false); }); }
Each time a CKEDITOR instance is initialized and ready, it automatically disables alt + 0.
There is a list of ascii codes for different characters here for reference if you want to disable other keys: http://en.wikipedia.org/wiki/ASCII#ASCII_printable_characters
Use the number in the Dec column (decimal) to disable them in the Glyph column.
source share