[FlyingShawn]

Ziggy's Excel method isn't working for me to fix the messages that already have a 2016 date (running a Sprint Mogul stock ROM, so I used the HTC official fix instead of Ziggy's workaround to correctly date new messages). For some reason, when I'd try to save the file in Excel it would mess it up (never figured out how, but PIM Backup would try to read it forever and never get anywhere), but I was able to workout a fix using Notepad instead:

1) Extract the .csm per Ziggy's instructions (to save time, I only backed up the text messages in that .pib and backed up everything else in another backup)
2) Open it in Notepad instead of Excel
3) Do a Find & Replace to change all 2016's to 2010
4) Save it using Unicode Text (it might have given the file a .txt extension, I don't remember, but if it did I just renamed it to .csm)
5) Upload it back to the phone and restore using PPC PIM Backup (don't bother putting it back into the .pib, PIM Backup can restore directly from the .csm file)

Hope this helps if anyone else is having problems using Excel to fix old messages!