actionscript 3 - Serialize class with version? -

if serialize class in as3:

var obj:customclass = new customclass();  var bytes:bytearray = new bytearray(); bytes.writeobject(obj); 

lets store bytes in database , retrieve them @ later date:

var obj:customclass = (customclass)bytes.readobject(); 

what if made change class in time. cast fail. there anyway differentiate between 2 bytearrays , determine change class has been made?