How do I add shortcuts that are not in the Shortcuts enum to my menu item?

To customize the shortcut (which are not present in the System.Windows.Forms.Shortcut Enum), you need to override the ProcessCmdKey event of the form and handle the needed keys. The below example has a menu item with name “item” and the shortcut Ctrl + Alt + 0 has been set by handling the ProcessCmdKey event. The Click event of the menu item is simulated.

//Override this method in the form which have the menu. This will only trigger when the form is on focus.
protected override bool ProcessCmdKey(ref Message msg, Keys keyData)
{
    if (keyData == (Keys.Control | Keys.Alt | Keys.D0)) // Ctrl + Alt + 0
    {
        if (this.Menu != null && this.Menu.MenuItems.Count > 0)
            this.Menu.MenuItems['item'].PerformClick(); // triggers click event.
    }
    return base.ProcessCmdKey(ref msg, keyData);
}

Instead of MenuItem, you can utilize ToolStripMenuItem which has plenty of features and all kind of shortcuts are available.