The asset drop-down doesn't support changing the search root but this can be done in other ways. There is a new URL parameter called rootpath that can be used or you can configure a symbol to be a navigational link and use it to set the search root. For example, you could create a second asset comparison table and configure it to list out each of the elements you want to use as search roots. You can then add a navigational link to this symbol so that when you click one of the elements listed, that element automatically gets set as the search root of the display. I'm not sure if the pre-release version you are running includes these features yet, but they will be available in the release which coming very soon.
That is helpful, but I was trying to avoid that since I have a large number of buildings, each listed under a parent "Site" element. The navigation link table would be extremely long in my case. Can you think of a way to programatically set the search root if I were to extend the already existing Asset Comparison Table symbol with a new custom symbol? I have never built a custom symbol yet and know that I would probably get lost quickly.