Have you tried looking through the localise tools for the stock era localisations? If you can find them and how they're set out, it should be fairly simple for you to rename your era. Another way might be to use Zerteds way to change mode names and icons for your era instead. Would that work? Its worth a try anyway.
Here's his tut:
Adding New Modes
At the end of the post he mantions that he got it working for eras too so that should help.