Word Basic? It has been a seriously long time since I used that, and its continued use has built-in obsolescence. I seem to recall that it is not fully supported in the most recent Word versions, but don't hold me to it.
Once the document has been merged the fields are replaced with the merge data, so you would have to split the line and delete the redundant information to get the required data.
Frankly I would bring your process kicking and screaming into the 21st century and use
http://www.gmayor.com/individual_merge_letters.htm. or
http://www.gmayor.com/MergeAndSplit.htm
to name your document from the data, with or without added text.