You could, for example, change:
Code:
.Text = "\([A-Z0-9][A-Z&0-9]{1" & Application.International(wdListSeparator) & "}\)"
to:
Code:
.Text = "\([A-Z0-9][A-Z&0-9]{1" & Application.International(wdListSeparator) & "9}\)"
This will limit the find string to a maximum of 9 characters. Such a limitation seems fairly meaningless, however, as few words would be longer than that and, if you have many parenthetic uppercase single words, those will all be included in the output.