Dim F1 As New XYZ with{.Sett=Test1}
Dim F2 As New XYZ with{.Sett=Test2}

Class XYZ
  Public Sett as Setting
 
  ...
  Dim a as String = My.Settings.Sett
  ...
 
  ...
  My.Settings.Sett="aaaa"
  My.Settings.Save()
  ...
 
End Class