OK, I tinkered with my old macro code here: https://forums.zotero.org/discussion/73159/announcing-zoterzero-for-author-only-cites


Now the following seems to work to remove all underlines from Zotero fields.

Function ZoterZeroUnderFix(F) ' Fix a field to remove the automatic dashed underline if Zotero automatic updates is disabled
''does not update bibliography or correctly disambiguate citations, just convenient to export a draft for review rather than waiting for full update
If InStr(F.Code.Text, " ADDIN ZOTERO_ITEM CSL_CITATION") = 1 Then ' make sure this is a Zotero field to modify, starts with right text
F.Result.Font.Underline = wdUnderlineNone ' remove dashed underlining from Zotero's delayed update feature if present
End If
End Function

Sub ZoterZeroUnder()
'
' ZoterZero extention: remove dashed underlines from all Zotero fields in document
''let's update all fields in document
''' based on http://www.vbaexpress.com/kb/getarticle.php?kb_id=1100
Dim rngStory As Word.Range ' vars for below
Dim lngValidate As Long ' vars for below
Dim oShp As Shape ' vars for below
lngValidate = ActiveDocument.Sections(1).Headers(1).Range.StoryType ' starting point
For Each rngStory In ActiveDocument.StoryRanges 'Iterate through all linked stories
Do
On Error Resume Next
checkField = rngStory.Fields.Count ' get the total number of fields in this section
While checkField > 0 ' check each field
changeSuccess = ZoterZeroUnderFix(rngStory.Fields(checkField)) ' check and fix this field
checkField = checkField - 1 ' check the previous field next
Wend
Select Case rngStory.StoryType
Case 6, 7, 8, 9, 10, 11
If rngStory.ShapeRange.Count > 0 Then
For Each oShp In rngStory.ShapeRange
If oShp.TextFrame.HasText Then
checkField = Shp.TextFrame.TextRange.Fields.Count ' get the total number of fields in this section
While checkField > 0 ' check each field
changeSuccess = ZoterZeroUnderFix(Shp.TextFrame.TextRange.Fields(checkField)) ' check and fix this field
checkField = checkField - 1 ' check the previous field next
Wend
End If
Next
End If
Case Else 'Do Nothing
End Select
On Error GoTo 0
'Get next linked story (if any)
Set rngStory = rngStory.NextStoryRange ' get ready for next section
Loop Until rngStory Is Nothing ' keep going through until all sections are done
Next
End Sub

I've tested it and it seems to work in Word on my Mac. I don't know whether it would always work for everyone, so no guarantees. Aside from the big looping action, all it does is checks each field to see if it's a Zotero field and if so it sets that field to not be underlined. To use: run the main ZoterZeroUnder() macro and it will automatically change all fields in the document.

Obvious warning: this is only for preview purposes and probably should only be used on copies of your document you're exporting as a preview.

--
This could also be useful, with minor changes, in the case that a user wants to make all citations bold, or something else along those lines.