I wasn't suggesting anything related to a parameter. (But I wrote more on that later.)
The approach I'm suggesting will (I expect) allow you to avoid much of the pain that comes from upgrading something you've customized. Instead of sending data to BBB, which it must figure out how to display, you send the complete HTML (all except a small bit that must be there to communicate with your app).
Read this for more information:
But if you're not comfortable writing code then this won't work for you.
Regarding parameters (or something similar):
If BBB were modified (as a new feature in 2.7 perhaps?) to allow a parameter to specify new divs to inject, then this could allow all sorts of customization that didn't require manually changing template files on the server and updating them again when you upgrade.
Perhaps better than parameters, BBB could have a folder (that is not touched during upgrades) that has customizations, and which are injected into templates. Each of these would need a CSS or XPath selector to specify where to inject the HTML, and it would need to have the HTML. These would essentially be partials (partial templates) but unlike normal partials, they would contain the address where they are injected instead of the containing template containing a reference to the partial.
I could definitely see the ability to inject templates being useful to a lot of people, including me.