Ok, maybe someone who knows more about this may be able to chime in, but...
First off, I doubt a factory reset would work. A factory reset just wipes all data, but doesn't actually revert your software version to its original factory version...it just leaves you with a refreshed, "blank canvas" of whatever software version you're currently running.
What you can do, if you can deal with a data wipe, is install the full RUU of the new MR2 update. This will pretty much do the same thing a factory reset would do, but leave you with the newest software version.
XDA post where I found the MR2 RUU (with download):
[RUU LEAK] Froyo 1.70.605.0 Radio 1.39.00.0627r - xda-developers
and the original source, with install instructions:
[Exclusive Download] Leaked 1.70.605.0 Update For The HTC Thunderbolt (No, It's Not Gingerbread)
Is there a way for you to upgrade the radio without losing data? To be honest, I don't know. I believe you need to be rooted to flash radio files, so I'm guessing the answer is no, but once again, I don't know the definitive answer to that question.