You might want to try to search for a program that can work with a blackberry backup idp file. I've seen several that can extract sms from the file, but you might be able to find one that can import sms and you can then reload that into the bb.
Here's something from the beta forum. Just read only but a post said it will allow editing in a future release. You might be able to find something like this that is already out there: New Blackberry IPD Reader