Try an OnExit macro like:
Code:
Sub If_Text()
Dim oTbl As Table
Set oTbl = Selection.Tables(1)
If ActiveDocument.FormFields("Text1").Result <> "" Then
ActiveDocument.Unprotect
oTbl.Rows.Add
ActiveDocument.Protect _
Type:=wdAllowOnlyFormFields, NoReset:=True
End If
End Sub