You can temporarily resequence the columns in the Mailmerge recipients
dialog box by dragging and dropping the column headers, but I know of no way
to make those changes stick.

Broadly speaking, Word tries to recognise field names commonly used in name
and address lists (in English, anyway - I have no idea what it does in other
language versions) and imposes its preferred sequence. If you use field
names that it does not recognise, Word seems to use the sequence used in the
the query. So one thing you can do is
a. put the fields you want in the sequence you want in the query
b. use an alias name for each field. A simple way that leaves the names
readable but does not appear to interfere with anything else is to prefix
every name by an underscore ("_"), e.g. use _firstname, _lastname etc.

(For example in the SQL you might have

SELECT firstname as _firstname, lastname as _lastname FROM mytable
)
b. prefix every field name by a number (say) so that Word will not
recognise it

Peter Jamieson