How to modify links href

I have a menu that only appears on a specific page. What I want to do is append #top to the end of each link’s href. Before you ask, the reason why I am doing this using code and not through the menu options is because I don’t want there to be a chance for the client to break this and also, in case the menu changes, this feature will still work on the new menu.

Any suggestions on how to accomplish this?

Thanks in advance.