User adding own dgnlib cuts out existing menu customisations?

As a user entering a new workplace/workspace I am wanting to add my own dgnlib containing MenuBar customisations. I can do this by either using the Workspace>Customize menu and appending my dgnlib or manually entering it into the ucf file such that it has a line reading;

MS_DGNLIBLIST > C:/User/User.dgnlib

This works and I can see my new MenuBar customizations, but I then find that the existing company MenuBar customizations (Menus) have dissappeared. I would have thought that simply using append(or >) rather than the "=" operator would avoid this scenario but it doesn't so I must be missing something?