Grab the WinXEditor from WinAero (https://winaero.com/comment.php?comment.news.30) and follow their instructions for adding/removing the shortcuts.

To add the accelerators (the underlined shortcut keys you get when you open the menu using the keyboard) simply rename whatever item you want to change the shortcut for and add a ampersand ( & ) before the character you want to become the shortcut. I.e. if I want to add "Control Panel" with the p as the shortcut character I would change the name to Control &Panel. Et voilà!