[pr0xZen]

You could always "export as single file", and replace the old paths with the new, with a text editor in the videodb.xml file (it will be in the root of your export folder). Then clean your library (after removing old source) before importing the database. Just make sure the "new" path in the videodb.xml file, is identical to the one newly added as a source in XBMC (in case you can access the source through multiple routes/accounts etc). I just went this route recently, worked out fine for me.

You might also want to take a look at step 5 in the link Ned Scott provided above - performing this will also import your previous watched statuses and resume points. Should go without saying, it need to be done before importing the modified database.