The multi-editor is a great tool when combined at queries to make large scale changes to your project. We were using it recently and discovered a quirk that I believe was just an oversight in the UI.
The multi-editor doesn't let you edit the mode setting of an effect. However, it does like to edit Render/Bypass which you edit in the same place. Combined with the fact that mode defaults to "Define Custom" and not "Use Shareset" this makes it a PITA to actually change / setup an effect shareset on a large number of objects. As a workaround, everytime we update the shareset we change every object again but it leads to a lot of churn on the files.