I don't know if there is code that can be added in this transition period to force a cache refresh, but it would avoid this kind of problem as people return to the site with their regular browser.
No. Without modifying the HTML of every web page, we cannot force browsers to refresh code that they have cached locally.
It is odd that we're one month out and people are still running into cache issues. Is there a specific server you were looking at? If we knew the server name we could look into the server configuration. Perhaps that specific server is sending overly aggressive cache headers for the .css and .js files included with the templates.