You can overwrite MOrder with a class like ChuckOrder. That class can overload MOrder and have a method like prepared. That method can be copied from the mother class and can be changed. A proposed core change can be to refactor the document action methods to build small blocks that you can use in your own prepare() method. That means that for your own changes you do not have to copy & paste the whole prepare()-method. That is bad style

Reference: http://wiki.idempiere.org/en/IDempiere_workshop_2015/transcript#Order_Document_Type_hardcoded_business_logic