With the help of this SO, you can do it to all ActiveX objects:
Sub EnableMultiline()
On Error Resume Next
Dim i As Long, oInShp As InlineShape, sTxt As String
For Each oInShp In ThisDocument.InlineShapes
i = i + 1
Err.Clear
With oInShp.OLEFormat.Object
sTxt = i & vbTab & .Name
sTxt = sTxt & " [" & .MultiLine & " -> "
.MultiLine = True
sTxt = sTxt & .MultiLine & "]"
If Err.Number <> 0 Then sTxt = sTxt & " <<-- FAILED"
End With
Debug.Print sTxt
Next
End Sub
You can check the output in the Immediate window to see which have been changed. Used On Error Resume Next
as there may be other type of ActiveX objects. After all, your goal was just to set the MultiLine property to True for all ActiveX text boxes.