Note that you can choose the scope for every shortcut by selecting "Use new shortcut in". One keystroke can exists for more commands, so when you select a new shortcut and press assign, Visual Studio can preserve this shortcut for an another command also.
The default scope is "Global", but "Text Editor" has higher priority in text editor, so make sure you select "Text Editor" under "Use new shortcut in:" in
IDE tools menu -> Options -> Environment -> Keyboard
dialog, before you enter and assign your shortcuts for VAssist.NavigateForward.