You could use the before_save event to interrupt saving and ask a question or two. This snippet in the Thisworkbook code module should get you started:
Private Sub Workbook_BeforeSave(ByVal SaveAsUI As Boolean, Cancel As Boolean)
Static Busy As Boolean
If Busy Then Exit Sub
ans = MsgBox("If you are about to save this as a text file and want the filename added to column A then click yes else click no", vbYesNo)
If ans = vbYes Then
Cancel = True
Set xxx = ThisWorkbook
fname = Application.GetSaveAsFilename(fileFilter:="Text Files (*.txt), *.txt")
If fname <> False Then
AColumnText = Application.InputBox("Is this what you want to appear in column A?" & vbLf & vbLf & "If not, edit it now.", "Column A Text", Mid(fname, InStrRev(fname, Application.PathSeparator) + 1), , , , , 2)
If AColumnText <> False Then
With ActiveSheet
For i = 15 To .Rows.Count
If Cells(i, 1) = Empty Then
Cells(i, 1).Value = AColumnText
Exit For
End If
Next i
Busy = True
.SaveAs Filename:=fname, FileFormat:=xlTextWindows ' I've only guessed at the fileformat.
Busy = False
End With
Stop
Else
' Stop
Exit Sub
End If 'AColumnText <> False
Else
Exit Sub
End If 'fname <> False
Else
Stop
'should save as normal here
End If 'ans = vbYes
End Sub
It only places one instance of your chosen text in column A in the first available slot below A14 (ie starting from A15) since you're not clear on whether you want the whole column filled with that text or not. Also see a comment or two in the snippet.
It leaves you with the file open as a .txt file but your save existing save routine may need to be used.