Hi Carl,
Word intentionally turns the Data Merge Manager on automatically to let
you know that you have opened a document that has merge fields in it.
As John points out, you can remove the MERGEFIELD Word Field Code from
the document and then the Data Merge Manger will not appear.
I think your question is whether or not there is a setting some place so
that you are not bothered by the Data Merge Manager's appearance because
you already know or don't care about whether or not the document is a
Merge document. If this is the case, then I believe that you can not
change this particular behavior.
-Jim Gordon
Mac MVP