I've been working on a map that has a lot (I mean a LOT) of assets that I don't want to use and I don't want to replace them with anything. So I came up with an idea to delete all of them that really works. In CM I marked the asset(s) as disabled. Open the map in surveyor and delete all missing assets. Save the update. Go back into CM and enable the assets I had just previously disabled. Done deal.