How can I import new SMS into my phone without wiping the current SMS?
I was able to use this answer and an SQL Manager I downloaded from the Internet.

Essentially, using my mad SQL skills, I browsed into sms table, did an UPDATE on _id field as per table structure of rerware Backup Pro to avoid primary key collisions, then did the merges per the linked answer. I later uploaded the database back into my phone. 

I'm doing a restore now.  If I don't come back complaining, it means it worked!

yep it worked.  I think I missed some SMS from a single person, but that was not related to the above machinations.